It's a concern that you even ask.
Absolutely!!
..as in a very short period of time...seconds.
If you have any reason to believe or fear you are too lean, a WOT plug chop should be approached with caution. Generally, you want to hold the bike WOT in as high a gear as you can get, under load, for a fairly large amount of time. A good 30 seconds, anyway.
That's about a gazillion times as long as it takes to seize a too lean bike.
That said, don't get paranoid about it. As long as your bike is in a decent condition (no leaks around crank seals, reed cages etc), the suggestions you read on this site as far as jetting will generally be safe to test with a WOT plug chop test.
Pay attention. If you hear detonation going on while you're WOT..back off! If you're concerned, run a shorter period of time (maybe 10 seconds) and check your plug. If it shows obvious signs of overheating (blistered insulator, shiny bits of aluminum on the insulator, or the grey-dust kiss of death (vaporized aluminum that used to be your piston) ) , richen it up!!
BTW, the 'color' you're looking for is way down the insulator, where it meets the plug shell. Looking at the tip up towards the center electrode isn't going to tell you anything about your air/fuel ratio.
Don't do it with a plug that's been in your bike for the last six months. Best done with a new plug (say the experts).