I'm wanting to paint a sunset on a cake but I've only seen posts about painting on crusting buttercream or fondant- has anyone tried painting on IMBC?

I haven't tried painting directly on the icing, I have used an airbrush and it accepts the color well. I would suggest chilling the iced cake until the icing is solid because it doesn't crust on it's own at room temperature.

Did you ever paint on meringue buttercream? How did it turn out left at room temp when time to serve?

fine -- no worries -- test it in your fridge with your weather & see how it goes -- it's humid here and I've never had a problem -- I used an airbrush on Swiss meringue buttercream

the only time I can remember that I had a problem was when I used edible ink markers and stuck the cake in the freezer for maybe 30 minutes before we took it to our daughter's -- holy moly that freakin' marker ink ran like disappearing waterfalls -- poof all gone except for mopping it up off the borders -- so for what it's worth 

Thank you! Do you think gel color mixed with vodka would run as well like ink marker?

no I don't think that would run -- I think your icing might need to be cold in order to withstand the brushing -- and I haven't tried this with  Italian mbc and I wouldn't say it crusts like American but Italian kinda gets a surface on it moreso that Swiss --

my problem with the markers was the extreme temperatures -- from the freezer to humid memphis -- duh, kate -- it was a family cake and blablabla I goofed --

i suggest you make the two meringue icings and spread some of each on a cookie sheet -- get it cold and see what's what -- I often use airbrush color too to dip & paint stuff (plus the alcohol)

would love to hear how it goes for you -- I think the temperature is key -- to keep the surface firm enough -- 

Thank you so much! I will let you know how it goes!