Only applicable to the 32-bit version of the Sims 3
Update – 30th August 2015
After a lot of testing by some wonderful members of the community we have finally managed to fix the graphics issue so all the affected Macs can now play the game. Please read this guide for instructions. Good luck!
If your Mac has Intel Iris or Intel Iris Pro graphics you’re probably finding it very difficult to play The Sims 3, if you can actually get the game to work at all. This is because the Intel Iris graphics are not supported by EA in the game and never will be as no further patches will be released for The Sims 3.
Apple started using the Intel Iris GPUs in the late 2013 model 13″ Retina MacBook Pro and all subsequent refreshes to date. The entry level 15″ MacBook Pro also has the Intel Iris GPU so if you have this MacBook Pro you will also be affected.
Most recent users are reporting that their games simply won’t load. Others have managed to get their games to sometimes load but can barely play as the graphics will start flashing and/or colours change to red and green, amongst other reported annoyances.
There is a workaround you can try though by editing the GraphicsCards.sgr and GraphicsRules.sgr files. Tmethei very helpfully posted instructions on Caspin’s Intel Iris thread over on the official forums. Some have had some success, some haven’t but it’s definitely worth a try if you’re desperate to play and your game’s not working. You can also try bypassing the Launcher.
Good luck!
Bluebellflora 
Thank you so much!
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This didn’t work for me. I’ve tried all sorts of things and I’m still getting the weird flashy game screen.
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