I want to try to make some IMBC but I'm a little unsure about how the color is going to turn out. I don't have any of that 'white-white' icing tint and no way to get any around here in the next couple of days. Soooo.....

I'm just curious, using organic butter (which naturally tends to be more yellow), how yellow is my icing going to be? It doesn't have to be perfectly pure, bright white, I'd just like it to not be an obvious 'light yellow,' KWIM? Would it be okay to use a little shortening in place of the butter, like maybe 1/2 to 1/3 of the total fat being shortening? Or is that even necessary? Maybe it won't turn out as yellow as I'd think, IDK. On cakes w/IMBC, they look fairly white, but maybe they were tinted? In some of the demo videos I've seen, the finished IMBC straight out of the mixer looks pretty yellow.

What to do, what to do?

Our farmers market hand churned butter is almost white. I can't help you on the color as my IMBC has vanilla bean specs and butter. But I never really noticed the icing as being something other than white. I use Land O Lakes. It is very white compared to my french buttercream made with yolks.

I just use regular butter and it always turns out pretty white...maybe a slightly cream color, but not yellow.

Add a touch of Wilton violet gel paste. It cancels out the yellow tint, don't go overboard, best to add it bit by bit.

Yes, you can replace up to 50% of the butter with shortening by weight. I do it all the time in the heat of the summer. Emulsified shortening if you can get it, but regular will work. I will help with the stability in the summer and it will lighten the color. Mine has never been yellow, but it isn't snow white.