1 M 1 F Thanks For The Quick Replys
Ok, 1 male and 1 female... but, are they in the same cage?
Because as has been stated already, they should NOT be kept in the same cage regardless of what their sex is. You need to have them in separate enclosures.
However, that still might not explain what has caused your male's colour change.
In general, colour changes aren't necessarily indications that anything serious is wrong. Chameleons go darker to absorb more heat, and they become lighter to reflect more heat.
However, they do also change to darker colours when they are stressed out.
In order to find out if anything could be distressing him, you will need to review your husbandry in more detail.
Use this thread to determine what sort of information you need to provide:
https://www.chameleonforums.com/how-ask-help-66/
We've already [possibly] determined that you are incorrectly keeping two Veiled chameleons in the same cage. But provide more details about your setup to ensure that there is nothing else going on that could be affecting either cham.