I noticed this some time ago, but thought perhaps it was my eyes playing tricks on me (and a teammate activated the turret before I could get a screen cap.)
Just got down to the jelly farm again, and the turret is indeed all gray with just slight shading.
I'll post a screenshot once Steam has uploaded it after I close my session.
Have you changed your graphics settings since you last saw it appearing "normally"? Some things like the AP/Sent's charge animations (the birds specifically) appear gray when set in compatibility mode(? not sure). Try fiddling with your settings if you run into it again and see if the color changes back to normal.
Otherwise it could just be a bad texture, where a reinstall will usually fix it :)
Pretty sure it's not my settings.
I run it on High settings pretty well cranked up. I don't normally have frame rate issues with a few exceptions, so I rarely turn them down and have never used compatability mode.
Unless the new Cull Transients option might be affecting it, I don't think it's settings since that's the only one that's changed in a long while.
If I'm there again soon, I will fiddle with the settings and see.
I saw this too, I run on high without Cull Transients.
Well I haven't seen it in person lately so it could've been changed... I just posted my usual generic-ish response for texture issues since it looked kinda odd. If multiple people are seeing it the exact same way, probably not a texture problem, so sorry for the assumption :x I'll check it out myself later when I can get back on.
Picture of the turret sans textures and a bee suit.
Also pictured: Toast failing at saying "huh" and trying to emote it first for some reason and feeling like a derp.