Coloring can be damaging regardless of your hair type. Permanent colors will cause the most damage to your hair and if you're trying to go for an extreme color change (3 shades lighter or darker than your Natural hair color), you could alter the Texture of your Dreadlocks.  Generally, the chemicals in permanent colors will cause dreadlocks to stiffen, but most of the damage is reparable.

tubbys colored dreadlocks
naaniMODEL Tubby's Tri-Colored Locks

After coloring, THOROUGHLY rinse your locks.  You want to remove any and all traces of the chemicals from your hair.  Some stylists recommend that you wash your dreadlocks at least twice with a Neutralizing Shampoo to remove any residue and to stop the chemical from processing.  Next use a good moisturizing shampoo.  Unfortunately, using shampoo after a color tends to "strip" the color and its vibrancy but it insures that you've removed any product that may have become trapped inside of your locks.  So the choice is yours regarding the shampoo.  To be on the safe side, you might want to shampoo your hair at least once.

Regardless of whether you shampoo or not, use a conditioner after rinsing your hair.  If you skip the shampoo step (and even if you don't) the conditioner will help remove the coloring products and reduce any damage caused by the chemical procedure.  Be sure to deep condition over the next couple over weeks/months and make sure your rinse out all of the conditioner thoroughly. 

MY FIRST COLORING ATTEMPT ~ DO NOT TRY THIS AT HOME
Ideally when coloring your hair you would go to a professional, but given that I know that many of you will attempt to do it yourself, I decided to be your guinea pig.  The above photo shows what happened after I initially screwed up my hair.  The final result was great but let me show you my first attempt.

Tubbys color mishapI have lots of hair.  Add that to the fact that dreadlocks tend to soak up product, this first color was a beast.  I made the mistake of applying the product to the roots far too soon.  I also didn't have a g
ame plan set in terms of where I would apply the three different colors I'd be using.

NOTE:  Be sure to apply the chemicals to the new-growth area during the FINAL 10-15 minutes.  Virgin hair will take color quicker and you'll want to avoid over-processing this area.

In the end, I had to do some creative fixing due to the overprocessing in the first attempt. The final results were just what I wanted (as demonstrated in the first photo).

I suggest you consult an experienced, licensed colorist if you desire to lighten your dreadlocks. If one is not available or you choose to tackle the project yourself, you can gather information on coloring here. Just remember, coloring locks is a very difficult process and requires skill and know-how that is best left to professionals.

Performing the procedure yourself may save money, but you'll probably regret it and end up having to go to the salon anyway...not to mention, if your dreadlocks are long and mature and you opt for boxed kits of color, at $6/box, you  probably could've gone to the salon as you'll need to purchase several of them.

Are Permanent Color Damaging to Dreadlocks?
In a word, yes.  But permanent colors are damaging to all hair, no matter what the style.  Heat's damaging too but you blow dry your hair right?  The threat of damage shouldn't stop you from coloring if that's what you want.  Colors can be fun.  If you're the type who's used to changing hair styles but are afraid to cut your locks, try coloring them before picking up the sheers.

Permanent colors are drying to the hair because the chemical process weakens the shaft and can cause the hair to become dry, brittle and susceptible to breakage.  This is why it's so important to deep condition thereafter.

Some argue that this drying effect actually helps promote dreadlocking because it removes excess oils and moisture and causes the hair to dry out and stiffen. Others believe that this chemical process weakens the hair and in some cases, slightly relaxes it.  They say that although the drying effect may prematurely speed up the locking process, the longterm effects may not be worth the initial success.

In the end, undergoing any chemical procedure will effectively weaken your hair...the question is how much and will your hair be able to bounce back?  In addition, as your dreadlocks mature, they generally become thicker which makes it hard to remove the color from inside the locks, so often the problem isn't the chemical itself but the residue that is left behind.  So rinse, rinse, rinse...

Tubbys second set of tri-colored locksWhat Brand of Color Would You Recommend?
If I had to recommend a brand, L'Oreal Professional Colors would be my all time favorite. I love the way my hair takes to the color and how vibrant it appears for weeks after.

When Should I Color My Hair?
If you've already started dreadlocking, it's best to wait until after you've reached full maturity to do any coloring. Reason being, you have enough to contend with.  Coloring too soon can add additional stress to your hair and psyche.  Not to mention, if you color in the middle of locking your hair and want to maintain that color, what happens when the new-growth starts to appear?  Will you recolor?  So wait until you're fully lock'd then go for it. 

If you have yet to lock your hair and want color, do it before you start.  Coloring loose hair is far less expensive and the results are far more predictable.

Whatever you do, remember...
Just make sure you rinse, rinse and rinse until all of the color is removed. In addition, purchase a faucet attachment that has a spray nozzle like the ones used in salons. By using a sprayer, you'll be better able to force the color out of your locks and reduce or elimate any residual effects. Just make sure the faucet you use has good water pressure...if not, the bathtub (even a waterhose) are great alternatives.

If you want to lighten your hair above 3 shades of your normal color, GO TO A PROFESSIONAL.  If you want blonde locks, don't attempt this at home.  You'll most likely end up with over-processed hair and locks that are damaged and thinning.