Last night I took out something larger (82mm refractor) as my main targets were two galaxies M98+M99. Here is result of almost one hour sketch. I started already at late twilight because I wanted to be done before rise of Moon. M98 was very elongated, larger powers revealed tiny rounded brighter core. The body was brighter along its western edge. M99 was very interesting, already at 42x I suspected an arm on the northern edge. The sketch exaggerate the arm visibility, It took me a while to figure out, how it was attached to the main body. There were two more brightenings south of core, one was probably an illusion due to nearby very faint star, second one seems to be another arm visible on images:
Really, congrats on the arms of M99!!! That's a decent catch. This past spring I observed the pair from in town and I got fleeting detail in 98 but 99 was more challenging so I used it as a requiring point for 98 to pass through again. I know it's a challenge to get those arms and times with the 8 under a mag 5 sky it was a total failure. Again, 98 to the rescue.
The blue you got in M15 is peculiar. I see it too with the 8 and it's not because I look for it, far from it. Indeed that blue comes to me and surprises when it does in it's conspicuousness - and then, like your experience, it too vanishes like it was never there. Now I've talked to other observers, one with a 16" and they saw if anything they see a yellow or slightly warm red view. And true to fact, measurements photometrically show those older red Giants - and to be sure, the blue members too.
My theory then, Alex, is this...
Small to medium aperture - we see the blue stars (collectively) (for real not just illusion) but it takes a bigger aperture to show the red because our night vision does not favor it at all. So in effect you need the extra power of a big scope to overcome our red insensitivety. The blue is real though - it just happens to fall into our sweet spot.
Funny because I DONT see that blue in M13 or M92. Just M15.
The haze you show accompanying the OCs, M37 being my fav is a necessary thing as that is our light sensitive rods revealing it's lower resolution which scatters the faint light Abit, hence the glow.
M11 was great. Saw that recently and beautifully so.