Graphicsgale -- I don't know.
In Gimp, Photoshop, PSP, ProMotion, and many other paint programs, there is a hex input field.
Anyway, you do not input them by themselves, you make an hex RGB triple like
#246dff
Which is a mid sky-blue.
IMO inputting hex colors is the quickest, easiest way to select from an old system's colorspace.
But, if you don't like that, you can also input the components individually into the numeric input fields.
In this case you will need to write them in decimal, so, in decimal, appropriate intensities are probably:
0 36 73 109 146 182 219 255