I have a Flolight 1024 Led panel which I like alot , I want to get a second panel and was thinkng of the cool lux 500, is it a problem to mix different brands of LEd panels ??

LED can vary from light to light not just by manufacturer. Also age of the lamp e.g. burning hours affect the colour of the lamp. The phosphorous coatings in the LEDs age with use and vary in colour temp as they age. The LED life is stated at 10,000 hours or even far more, but they may not stay a usable colour that whole time.

I suggest take your current LED light with you to compare the colour temp when buying your new light.