Skim producing different color..

[DracoKat]

For months my skim has always been brownish grey, thick and yucky.

I noticed the last two times I cleaned it out, it's more green. algae green color.

What would cause the color change? nothing different has been done to the tank.. no new supplements or livestock

 

[psirex]

Change in food? More noticeable algae in tank? Is the sump area lit?