How do you clean your PCB after soldering

Hi.

I get my PCB from JLCPCB

Just finished to solder a small batch of circuits. They are power supplies, tracks are big and I have to heat high. But I have this challenge for all my boards. After I cut the extra lengths, I need to clean the flux. I use IPA. The fabric leave traces qbd fluffy stuff.

So my question are: - How do you clean your boards after soldering? - Is black PCB not good. Is there another colour I should use instead of black? - when I use PCBA, the board are nice and clean. How do they do that?

Thank you for your help