Is it possible to make webgl's background transparent in Linear Space?

I know its possible in Gamma Space by following the knowledgebase:
https://support.unity3d.com/hc/en-u...79.1797063557.1584675360-724054719.1584675360

however it falls in linear space, here is what i found:
1.GLctx.clear(mask) seems not work, the background is black after calling GLctx.clear(mask) in linear space;
2.GLctx.clearColor(0,0,0,0) seems not work, when i try to modify the clear color, it remain the same (0,0,0,1) even i call this method to change the color;

i try this in unity 2017.4~2019.3, the result is the same, any ideas?

 

https://answers.unity.com/questions/1512853/how-to-make-background-transparent-in-unity-webgl.html
There is this question also.

I want to Linear color space and transparent background.
Is there a relation between color space and GLClear?

In gamma color space, transparent background works well, but linear is not work.
Unity 2018.3

Thank you.

 

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