Contrary to popular belief chameleons do not change colour to match their surroundings. Their colour change is affected by hormonal or mood changes and is a reflection of nervous activity. The colour change is a means of communication. Changes occur when they are frightened, sexually receptive, carrying eggs, courting etc. Their 'calm' colour pattern is usually the only one that is likely to be an effective camouflage colour. So, to answer your question, a blind chameleon can still change colour the same way as a blind human can still speak because this process is nothing to do with it's environment.