Are you talking about useing the _color key? If so then use _color as the key and 1.0 1.0 1.0 as the value. It goes Red (0.0 - 1.0) Green (0.0 - 1.0) Blue (0.0 - 1.0). If all three numbers are the same you will get a grey scale with 0.0 ,0.0, 0.0, as black 0.5 , 0.5 , 0.5 as grey and 1.0 , 1.0 , 1.0 as white. If the numbers are off you will get a color, 0.5 , 0.6 , 0.8 would be a greyish blue-green for example, or 1.0 , 1.0 , 0.0 would be bright yellow ... it is simple to do it in your head and get the color you want, however you can convert from a normal color value to the 0 - 1 value, it tells you how in the shader manual in radiant.
"Assassination is the extreme form of censorship." George Bernard Shaw (1856-1950) I put the new in b.