Colour system and changing header?

[NedFlanders]

[Sorry for making so many threads ahhhh]
Hi everyone, I'm wondering if there's any way to do these things.

I'd like a system of pets where the pets can come in different colours; eg; body white, belly green, and markings pink (basically exactly like Flight Rising's system) how could I program it so users can first pick their animal and pick the base colour of theirs, and the other two are randomised? I would also like a breeding system like flight rising's where the colours of the two parents determine the outcome of the offspring? How would I program this? And how would I make the art into it? Would I have to individually colour every single colour and marking option?

I would also like to know how to change the header. Say my website had an image header of one of the in-game locations; I would like this image to change according to the ingame time; eg; at night the header image is set at night, at dawn it looks to be early morning, etc,,, basically I would like the image to change according to the time, about four times a day.

Thank you!