Basically the genes that code for all-white rabbits with red or blue eyes "turn off" all the other color genes, so you can think of an all-white rabbit as a colored rabbit with whitewash spread over the color.
Almost any color can "hide" behind a red-eyed white (or "REW") or blue-eyed white (BEW) rabbit. If you breed REWs together, you
should always get REWs, and BEW x BEW
should always give you BEW.
But if you breed either one with any other color, you never know what you'll get (unless you have pedigrees for both parents, in which case you can make some guesses). You might even get some spotted bunnies!
Your siamese rabbit is probably a siamese, a siamese sable, or a pointed white. You can tell the difference between a siamese/siamese sable and a pointed white: the first two have brown eyes, and the pointed white has pink eyes. As it turns out, siamese and pointed white are two of the few colors that can't hide behind REW or BEW, so in terms of color variations, you basically hit the jackpot!
Gray is a color that could describe a number of varieties. If your gray rabbit has different colors on each hair, that's called chinchilla. (Your white rabbit with brown eyes is probably a color called ermine, which means it has genes for chinchilla and for self/solid, so I'm guessing your gray rabbit is a chinchilla.)
Pull back on or blow into the fur to see if it's got separate bands of color (chinchilla), or all one color which shades to lighter as it gets closer to the body (called a blue, or a self blue).
Here's a chinchilla:
View attachment 32714View attachment 32717
Here's a blue self/solid (note her eyes are not actually red, that's just an artifact of the flash):
View attachment 32715
The image below is obviously not a blue, it's a red, but it's what self fur color looks like underneath - no rings:
View attachment 32718
If the coat is gray-looking but the rabbit looks like it's shaded towards its extremities, it could be a smoke pearl, siamese, siamese sable, sable point (the sable colors are more brownish but could still be called gray).
Smoke Pearl:
View attachment 32728
Sable:
View attachment 32719
Sable Point (a dark one):
View attachment 32720
And here's a pointed white, also called californian or himilayan (note the pink eyes):
View attachment 32726
That's probably enough info to make your head spin. If you could post some photos of the rabbits, we could probably be more help.