What video card and display driver version do you have?
This information is available in the Photoshop Help - System Info dialog.
-Noel
NVIDIA GeForce 9400M:
Chipset Model: NVIDIA GeForce 9400M
Type: GPU
Bus: PCI
VRAM (Total): 256 MB
Vendor: NVIDIA (0x10de)
Device ID: 0x0863
Revision ID: 0x00b1
ROM Revision: 3448
gMux Version: 1.8.8
Displays:
Color LCD:
Display Type: LCD
Resolution: 1440 x 900
Pixel Depth: 32-Bit Color (ARGB8888)
Main Display: Yes
Mirror: Off
Online: Yes
Built-In: Yes
Given that it's a Macbook, then you don't have the options a PC user would have for updating display drivers separate from the OS.
You might try going into Photoshop - Preferences - Performance, clicking through the [Advanced...] button, and try selecting a different GPU mode, or even turning off the use of the GPU entirely. Remember to fully Quit and restart Photoshop after making any changes there and before testing.
Does your system have dual GPUs? I have heard that such a setup can confuse Photoshop, and that disabling the low-power GPU via the Mac system configuration can be helpful.
I'm more a PC expert; perhaps a Macbook-familiar person can add some advice here...
-Noel
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