Hard to answer. Yellow legs are fairly easy, as white is dominant over yellow. The problem is that yellow and blue legs can hide under white legs and pop up again and again down the road. The only way to know for sure is a process of test mating. Just always make sure you never breed yellow to yellow or blue to blue and try to avoid breeding birds with yellow and blue legs if it can be helped. Sometimes it can't be helped though.
I am not sure what you mean by face shaded with color? Do you mean dark faces like a sumatra? Do you mean white in the earlobes? Either one of these things will be very very hard to get rid of. White earlobes seesm to be a very stubborn, persistent problem. Even when using parents with all red lobes, it still pops up all too often. Just don't breed white to white or white at all if you can help it, but, if I have an excellent size and type bird with blue legs or white lobes, I will still breed it. Thats just me. I feel conformation and size trump color.
High tails are actually pretty straightforward for me. As best I can figure, the long tail itself is dominant, but the well spread and low carriage part are recessive, or mostly so. Mostly-lol-I have had high tails pop up from perfect lobster tail parents before.... For me, the high tails has been the easiest area to make progress. The white lobes folllowed by off color legs has been harder to fix, but, honestly, part of that is because I've made a concerted effort to get the tails down the past 2 years, and have not made the same effort with ears and legs. I've personally chosen to fix the overall conformation first, and worry about color later.
Edit I was typing this as Saladin was and he beat me to it....
