Take a look at John A book, polished poker there is really useful chapter on how to make good notes, harrington also have it at online 6 max cash but it is a bit more complex...
When i was playing on PKR i was tagging players with little icons, they had a little fish icon, little shark icon, and all sort of different icons which you can use to remind you on whatever you want... I mostly used fish icon to tag really bad players and look for them later...
About how i take notes first thing that i do is that i write down first suspicious act that someone to at the table, betting patterns, min donk bet, really smal turn bet river over bet etc. Also if someone opens from UTG with 2bb and later with 4bb make sure to write it down, this my friend is betting pattern, most useful online tell, if somehow you manage to see his hole cards at showdown write what cards he had, that doesn't mean that you should pay every street just to see his holdings, at micros there is always someone to do that instead of you, you just need to pay attention to what happens on the table even if you aren't involved in a hand...
As for the color labels i see some people mark fishes as blue and regs or tag with orange or brown (me personally mark tags and regs with red, means avoid
), it is really the personal choice just dont mark reg and fish with the similar color so you wont mix them up when multitabling that could cost you money