The interior is done easy enough, but somewhat lengthy process. I converted mine to blue. Granted, different car, but GM still behind it. The original lighting in my car was accomplished by using a yellowish white incandescent bulb with blue covers which (once it hit the switch surface) resulted in the stock lighting "beige" color.
I did a lot of the work myself, but some things which were more delicate/difficult I left to an expert. So, my dash cluster and my HVAC controls were done by someone else. I did all my switches myself (window controls, lock controls, dimmer/headlight switch, foglight switch, and traction control switch). It was a *****, to be honest. I soldered LEDs so they won't ever burn out.
End result:
(my steering wheel controls are what the stock lighting used to be, and I've since dealt with them)
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2004 Impala LS - got some mods
NAIOA Moderator

Making you think twice before picking on Impalas