The FlashForge Dreamer uses G-Code to control the RGB lights. The G-Code line for the default profiles is highlighted in the picture below which is for the Starting G-Code in the process settings window. The lights are set to red for preheating and off for the print, but I personally like to print with the lights on max so I set the zero's to 255 for each of them. 0 is off, 255 is max for each RGB value.
M146 r255 g255 b255; max lights