A lot of reference you find online is going to be over-edited garbage that will teach you all sorts of bad lessons about colors, values, etc.
I put out a free pack of mostly landscape reference that's minimally edited and great for studies: https://t.co/bxzQCGSAVm
Do as many 30~ minute color studies as you can
No color picker, don't worry too much about details, just get the big shapes and colors
Few things will teach you better to capture a sense of light in your work