I've been testing things out for my maps and I came across a problem,
My gel seem to render unusually, when going through portals.
And my brush seems to be dark.
(No it's not a vertex texture)
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I can help with one point. The brush being dark must be caused by it starting below the ground, thus receiving no light. It generally helps to have it spawn in the open position, and then closed if possible.

I have no clue about the gel, though... never seen that error before.

I have seen the error before. My gel also renders strange whenever going through portals on thin surfaces.

This happens because the gel's renderer actually renders the gel slightly behind the portal then ejects it out, but because the surface your shooting gel out of is so thin it can't hide it there and defaults to drawing it stretched to the portal. Once it's out of range of the portal the error is fixed. (The distance between gel and portal also seems to be a difference - bigger gap = less chance of this occuring) The easiest solution is making the panels the gel comes out of thicker.

@Random
I tried making the panel in open position and closing it at map spawn, and it worked.

@BrainstoneX & Groxkiller585
Making the panels thicker to 8 units worked, and moving it far away from the gel worked too!

Thanks for all the help.