Possible way to change
Well not to bring this up from a post quite a while back, but i tinkered around with the A/C control unit when installing my headunit, and i found the bulbs to be twist lock miniature dash light bulbs.. if you can measure the bulbs size, then i think you can switch out for a diff color. I've found white, blue, amber, red for this twist lock bulb. I've been wanting to switch mine out for white, but i'd research first.
BTW if anyone has had a 03-05 Instrument cluster pulled out, please check what bulbs illuminate the gauges, because i would believe Toyota would have used the same type of bulbs.