@Senior_Vagabond That is a great question!
Yes, indeed when you have mis-matched colours in a 2 or 3 gang box, it just doesn't look great.

You are clearly a bit of a perfectionist - like me! It's the sort of detail that many won't pay any attention to, but for me it would constantly be an irritation aesthetically even if functionally perfect. 
I know we can't have everything but I wish alternative decorator colours were available - my kitchen switches are black with Stainless Covers and I had to use an alternative solution utilizing a Black Decora 'dumb' switch with a different type of device. 

On the initial question, I recently installed a 'Legrand' switch and I would believe it to be very similar bright white to the Kasa - I don't have a side/side in a common multi-gang box unfortunately but will try to get that for you (I need to to swap things around - it was purchased to replace a switch in another single gang location, but I can swap it with another older switch - which IS mismatched) to a 2-gang box with a HS210