In the days of indoor smoking, most white surfaces quickly turned yellow with nicotine from the burning tobacco. Odds are pretty heavily in favor of those desks down below having ashtrays.

Since early (before orthochromatic and panchromatic) emulsions see only blue light, things that are blue are rendered lighter. The opposite color of blue is yellow which shows dark since it's the absence of blue.

If the stars material had yellowed or was a warm, yellowish white like a cream color, that would show up as dark.

So, yellowish stars on a blue background become dark stars on a light background.

Is it some odd effect of the photography process (as with the oranges a few pix back) that makes the flag appear to have dark stars on a light background?

Also, the star pattern appears to be that for the 45-star flag (used 1896-1908), rather than the 46-star flag (1908-1912) or 48-star flag (1912-1959).

[Good eye. You're right about the date. Now changed to circa 1908 instead of circa 1913. As for the stars looking darker than their background, that's a good question. The emulsion on 19th-century glass negatives showed blues much lighter than later panchromatic emulsions, but that wouldn't explain the dark stars. - Dave]