This symptom (dim display, color cast) is typically a function of the backlight going bad. Apple's solution is to replace the entire display panel, which is quite expensive. It is also usually unnecessary.
Replacing one or both of the backlight's key parts (the power inverter or the CCFL lamp-element) is usually sufficient. Installation is a bit tricky, but is not hard if you're comfortable working with a soldering iron on small parts.
A web search for "lcd repair" will reveal many stores that can sell you a replacement parts, and some that will even do the work of installing them. Replacement lamps appear to cost $10-20 each. Replacement inverters appear to cost $50-130 each. Companies that do installation charge a wide variety of prices.
