The text that goes in the color tag gets put straight into the browser as this:
<font color="color">bleh</font>
Due to the unusual scheme browser makers have come up with for determining color names, colors that are not recognized will be completely random.
Watch:
turquoise
[color=blue-green]blue-green[/color]
mauve
Turquoise is the only one that actually works.
If you want a color that stays the same between all browsers you gotta stick with simple ones (red, blue, brown, black, white, etc) or use the hex code, e.g. for red, #ff0000 (DON'T forget the #)
The codes are each two hexadecimal numbers and the set goes in order from red, green, and blue. If you don't know hexadecimal, here's a quick run-down:
00 is 0, aka minimum
40 is 25%
80 is 50%
C0 is 75%
FF is 100%, aka maximum
For a completely green font, use #00ff00, for a completely blue font, use #0000ff. For yellow, #ffff00. For orange, #ff8000. For magenta, #ff00ff. For purple, #ff0040 or #ff0080.
You can also pick a color from a paint program such as Photoshop or PSP and it will tell you the hex code for that color. (you might have to pick the color and then click the little box that shows you what color you picked to get the screen that shows you the hex code)