Okay, sort of embarrassing, but maybe my misunderstanding will help someone else in the future.
The sight glass is clear, and there is a white shield behind it. When the hydro fluid is part way up the site glass, one can see a slight color variation between the white shield and the light yellow fluid, but when the fluid is over filled as mine is, the site glass looks like the yellow plastic of a weathered headlight cover. which is what you see in my picture above.
I parked my tractor on a side hill this afternoon and was able to see the white shield clearly, which then also let me see the colored fluid when I went back to level ground.
Crisis averted, all looks good.