what are you usign to create the image I do not get the same issue
for my blue rectangle (0x0000ff) I get 0xff as expected
or can you send me the image you are having problems with?
I now get your problem using MSPaint
if you create an image in MSPaint filled with 0x0000ff and open it in flash flash thinks it's 0x0000fe however if you open it in photoshop you get 0x0000ff
here are some other posts on the issue (with no solution)
oddly you don't get the same problem if you embed the image only if you load it using Loader