I believe Basilisk only offers the video modes supported by the video card of the machine you're running on. Most likely your video card does not support 256 color mode (this is pretty common these days).

Hope that helps!

Mmmm, I'm sure it dcepends on the OS and Mac you're emulating. Think this has been said before, don't expect support for millions of colours if you're using a Mac II ROM, and vice versa. I have no trouble in Basilisk II getting 16 colours so I can play CC's Patton Strikes Back, I just have to use System 7.1 on a IIci ROM.

Yes, I would second bertyboy. There are some strange SDL obstacles preventing to use e.g Thousands of colours on some hosts, but in this case I would suspect ROM and BII settings.
I can confirm that BII build 142 and the newer builds will work with 256 colours in Windows7-64 Ultimate.
BII is set to MacII, System D1-7.1, 1MB ROM from a Quadra.

And if it's not in the Basilisk II Help Guide here, it should be, keep it sensible when tinkering with your BII settings, ie. don't emualte a 68040 with an m68020 ROM, and so on. You have a blessing in Windows (over the Mac version) that you can set up multiple directories and multiple settings files and keep multiple emulated Macs with different OS's on your PC, you just need a single boot drive image for each and a single "monster" drive (maybe even as big as 4GB) that is used by all the environments for holding all your games and apps.

@Dimitris1980:

There is only option for million colours and i cannot play some games that require 256 colours. What can i do?

On Windows, I use the no longer supported, "Build 142" of Basilisk II by Lauri Pesenon. It has a more highly configurable GUI and some features I can't do without that aren't available in any other port of BII. Such as a fixed IP address for the emulator, a choice of about 25 different models of Macintosh to emulate, and setting the display, to 1 bit, 2 bit, 4 bit, 8 bit, 16 bit, 24 bit, 32 bit colors.

Caveat: I don't know if the 142 build runs under Windows 7 as I haven't used this OS, still on XP here. Want to be a guinea pig? Look for "Basilisk II for Windows build 142 (a much older version from 2001)" in page.

[Edit] posted the above, before reading 24bit's

I can confirm that BII build 142 and the newer builds will work with 256 colours in Windows7-64 Ultimate

So I guess its OK for Win 7, too.

This is excellent news for me too, to know BII build 142 isn't broken under Win 7. There's hope for me yet should I need to go the Win 7 route

Thanks for getting back with your results. Cheers.