Colours and the words they modify
I'm still unclear about whether to add and "e" to the end of the name of a colour. If the word has feminine gender, you add an "e" to the end of the colour and if the word is plural the colour also gets an "s" at the end. Is this correct? It seems that some words can themselves be either feminine or masculine, such as "chat" or "chatte". Again, how do you know which gender to use, since this will, in turn, change the modifiers.
Here is a link to a webpage that makes the changes clear. Several colour words have irregular declensions.
Colors don't modify words. They are themselves modified according to the words. If the word is masculine, you use the masculine form of color, the same is with feminine and the corresponding plurals. As to the nouns' genders, you have to memorize them. I am Russian. We have genders too, but they don't agree with French or German ones.
I'm not sure either, though I think in the case of chat/chatte is depends on the context i.e. whether one is talking about male, female, mixed, or indeterminate cats. I really need to get a French grammar book to look these things up. I have some Spanish grammar guides and they are extremely helpful.