No usable "Red Yellow Blue" colour scale exists, whether in Excel or anywhere else. Red & Blue are primary colours, while Yellow is secondary, made by mixing green and red light. The two commonest colour scales are Red, Green, Blue (Excel VBA has an RGB function) and Cyan, Magenta, Yellow, Black (Excel has no equivalent I have met). Excel also has facility for entering a colour as an integer in the range 0-16777215. Finally, Excels up to 2003 (I don't know about 2007 and later) have an internal colour palette of 56 colours that are configurable on a per-machine basis.

Regards,

John Davies