If you use NeoGamma, then patching the .iso will make it worse. Also forcing the game to use NTSC video mode while it's actually a PAL game, reduces the compatiblity. If you get black&white playback, the game is WORKING, but you have a video mode problem, and then ask about that.
You may need to force a language that is actually present in the game and/or enable Country String patching. Both could also make it worse, so only enable it if you know you need it. And there's some games that can only be played if the system menu region actually matches, you may need to google for game specifc solutions in that case.
Converting the .iso's region is only useful if you:
have a modchip, actual retail import discs, and/or cioscorp/darkcorp
AND
you DON'T have priiloader
And the region conversion only changes the info that the game is from another region, which doesn't fix any video mode problems, only makes them worse. Some region patchers also patch the video modes, which might be useful for black&white issues. But the video mode patches in NeoGamma should be able to do the same, and on some games they cause trouble.