If the collection cup is adjustable, you need to raise it up so will be skimming 'dryer' and will get more brown skimmate.
Currently you are skimming what is considered 'wet'.
Then it's either one of 3 things - you don't have much to skim out of your tank (meaning it's extremely clean), or you may not be adjusting it correctly, or you need a stronger/better skimmer.
What size is the tank and how many fish are in it?