Normally, macs have a very nice color calibration tool that corrects for color cast of the screen, gamma adjustments that are not constant at all brightnesses, etc. This gives a very good, color corrected screen. (It doesn't do a good job of white point correction, and it requires you to use a LAB-style control to adjust, making it hard to get R, G, and B all neutral at the same time).
When UfoAI starts up, it forces a pure single-gamma-only adjustment, and wipes that color correction out. This gives a strong color cast on my system because the monitor doesn't have accurate color reproduction. UfoAI forces a color correction of "Monitor neutral", with gamma (and in 2.3, lightness and contrast) as the only adjustments possible.
In the current (trunk) revision, this color forcing is only done once, at the start up of the game.
In revision 22268, this color forcing is done every time through the main loop of the game.
Now, I can turn the nation borders on or off, no problem.
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The geoscape problem isn't directly caused by nation borders being on or off. If the setup is bad, then it's bad. In the trunk version, I can start loading Ufo, wait for the colors on my screen to change, start the system preferences -> monitor preferences, and get my corrected colors back, and wait. Eventually, Ufo starts, and things work fine.
However, if I use the F8/F9/Alt-tab controls after starting Ufo, then the geoscape will be messed up:
1: If not yet displayed, then when it is displayed.
2: If currently displayed, then when the nation borders toggle is changed
3: The results after a battle are not tested
4: I just realized that although going into base view, and then back to geoscape view does not fix it, I haven't tested if that causes the problem to display.
The problem basically looks like "Almost random" junk is used as the map picture...except that (1), it's oddly patterned (it looks more like some weird ascii-art dump, like when a printer that should be printing graphics goes into text mode somehow), and (2) the pattern changes slightly, and consistently, as you move closeup/far away on the globe.
I suspect that "spaces" (F8, the multiple desktop manager) is the cause, but haven't yet tested that specifically.