Would it be out of line to put on my BDU's (they are reg) and salute our flag at 1500? The flag is out doors and stationary.
Sure...go ahead.
I wouldn't have, not that I haven't put on my uniform for Memorial Day in the past... but now that I know better... CAPM 39-1 Table 1-1. is really pretty restrictive on when you can wear your uniform.
The best person to ask this is your squadron commander. BTW, you don't have to be in uniform to pay proper respect to the colors.