Gulf Racing Blue

This was about all I could find on a GT40 forum.

Powder blue (PPG 12163)
Topaz (orange) (PPG 60812)
Royal Blue for thin stripe between orange stripe and powder blue (PPG 13126)

OR

You can use Porsche colors. The codes are:
Gulf Blue - Porsche 73 - Code 328 or J9
Gulf Orange - Porsche 72-73 - Code 019
For Royal Blue you can take a Dark Blue

Go to Model Car World Automotive Finishes. They have EXACTLY what you are looking for.
http://www.mcwautomotivefinishes.com/

Excellent!  Thanks to you both.

Regards,
Bruce

Mix it to match.