Image effect have weird color on iphone 5C

Graphics Shaders & Materials
1

I’m making an image effect, which processes the screen and save it to a render texture. It work fine, but user report it look wrong on iPhone 5C(work fine on others iOS device)
On the right is how it should look like, on the left is how it look on 5C:

1396×1334 265 KB

As you can see the color of the background look really strange. What might be causing this issue?
I’m suspecting render texture format(I use the default one) might be the culprit, but if so it should happen on all iOS device, should it?
It could also be my shader, but I have never seen image effect causing something like this before, especially when it does not modify the color, just alpha-blend another color on top:

2

Remove your implicit casts to get more reliable results cross-platform.

float3 outRGB = srcRGB * srcA.xxx + dstRGB * (1-srcA).xxx;

3

That just the algorithm, not exact code. But I do use implicit cast everywhere so I will check that, thanks!