creo3 config.pro option documentation for: SYSTEM_LETTER_COLOR
system_letter_color
<0.000000 0.000000 0.000000>
Specifies the default RGB color for datum tags. The three real numbers from 0 M-^S100 specify a percentage of red, green, and blue, respectively, in the resulting color. For example,0 0 49
specifies a medium blue.