:)

Most fans of SU ship blue and yellow diamond, and as a result of that ship, there’s many variations of green diamond.

But as we know from the “change your mind” episode, yellow and blue are not white diamonds because their gems absorb the colour of the other. Blue’s gem absorbs the yellow, Yellow’s gem absorbs the blue.

So if they fused, would they actually form green, or would they form some kind of new and improved white diamond fusion? They could each bring the hue that is absorbed in the others gem and thus, they would both have the full spectrums when fused as one.

But the show uses subtractive colors as their base for design... mostly??? It's a nice idea they both are White when fused, since Yellow is a mix of green and red and Blue is the other primary color. But even if the show goes more by designing with subtractives, White says she’s all the light spectrum, so... taking only that into account, then yes, Yellow + Blue = White!!!

But also, if that were the case, A LOT of fusions would be White :o

So each two Diamond fusion between Blue, Yellow and Pink (OR Steven) would form the according secondary color (green, orange, purple). But if the three of them fused, it'd make another White Diamond. Another White Diamond that I'd assume, would have the opposite of White's personality as it's the three others added together, possible exaggerated.

Then again if all four Diamonds fused, aka, the real White Diamond and the fusion of Blue, Yellow and Pink, they'd neutralize each other and we'd get a Black Diamond, the absence of light.