Blender Git Loki

BGE: Fix T43822 Videotexture does not use sky color for off-screen
rendering

Make scene background color as default for render-to-texture instead of
current blue color (0, 0, 255).

It is very useful for mirrors setups.

Reviewers: moguri, ben2610, sybren, panzergame, hg1

Reviewed By: panzergame, hg1, moguri

Subscribers: mpan3

Differential Revision: https://developer.blender.org/D1287