It's simply a matter of changing the panel lights in the Aircraft.cfg. The trouble is you might not have an acceptable panel light in your Effects folder; depending on how long you've had FSX and how many downloads you've made.
With FSX running in windowed mode, open your FSX/Effects folder and look for panel lights. Note the filename of one that looks interesting ('B747_panelwht', and similar). Now open the .cfg of the aircraft you wish to change, scroll down to the [Lights] heading, find the panel light, and replace the existing filename with the new one. Now return to FSX, restart the aircraft ([CTL]-A, A, [Return] and see if you like the effect. If not, pick a new light and keep trying.
Hope this helps.
