Mike,
So far we've been really lucky. There has always been a few shingles to replace, so I pick a couple of the worst ones right under the ridge cap and remove the old shingle then I have some hoops that bolt into the roof with 4-2½ lag bolts. From there it's the good ole ropes and harness. So far this system has worked well. The job I just finished my helper put it thru the ultimate test, he slipped at the peak on wet wood and hit at the bottom of the roof line at mach 1. Everything held up great except his legs, they were so shakey after that we took a super long lunch to calm the nerves. I also have better luck with very soft flat soled shoes, they seem to stick better than the standard work boot. I'd like to get a pair of rock climbing shoes to try out. If the roof is steeper than a 6/12 it's time for boom truck.
As far as the roof color goes it is different with the age of the shingles. The older the shingle the more brown it turns.
Jim