LED Dimmer Unit

This is a revision of a previously posted project. Now I require a completed working unit that will sequence the illumination of three banks of LED's. The three banks will be of different colours RED, WHITE, GREEN. Each bank should be switched on in turn, however I do not want the LEDs just to switch on and off they should be increased in intensity from Off to Full On to Full Off again. Eg All Off Red Increases to Full Red Decreases to Off White Increases to Full White Descrease to Off Green Increases to Full Green Descreaes to Off Return to Start again. Full cycle time should be around 90 secs The LED's are in banks that require 12v DC, to dim them the circuit is required to pulse between 12v and 0v to give the effect of dimming by altering the mark/space ration. Max Current per LED bank approx 500ma.