Fix /camera fade colors + add alpha

Description:
In the Bedrock Edition, the /camera fade command currently has the issue that the specified color (<r> <g> <b>) does not work. No matter what values are entered, the screen always fades to black.

This makes the command much less versatile, since for cutscenes, minigames, or adventure maps, specific moods through color transitions should actually be possible.

My suggestion:

1. Fix the bug so that the provided <r> <g> <b> values are actually applied.

2. Add an additional <a> parameter for the alpha value, to allow flexible control over transparency/intensity.

This would allow creators to design much more creative effects and transitions.