This is actually a macOS/Color Profile issue… I dealt with this issue and a client last week… and to prove it’s not a JUCE issue I created a test app and demonstrated to them that drawing a Photoshop image inside of JUCE and also opening it in Preview shows the “wrong” color:
In this image is the PNG opened in Preview (top left) and painted in my JUCE app (top right) and a filled rectangle painted in JUCE (bottom right).
Color Toolkit shows the value for all three on Mojave on my iMac in the bottom 3 values. The PNG was created in Photoshop and the color is 0xFF12403B. Interestingly enough GIMP shows the color value in its picker as 0xFF12403B.
I tried adjusting the Color Profile on my iMac and it didn’t change the value.
If I do the same test using macOS Lion (10.7.5) in a Parallels VM then all colors show as 0xFF12403B on the same iMac.
Rail