RichTextLabel BBCode Rainbow animation can't be played backwards or paused

[havi05]

Godot version

v4.2.rc1.official [ad72de5]

System information

Windows 11, GeForce GTX 1660 Ti, Forward+ render

Issue description

The BBCode rainbow animation can't be played backwards correctly. Not all rainbow colors are shown, if the frequency setting freq is negative. (It seems that just magenta and red are moving) If the setting is 0 the animation should pause, but the whole text is just red. (Not shown in the video, but in the MRP). Here is a link to the documantation with all the settings for the rainbow animation.

2023-11-17.22-23-41.mp4

Steps to reproduce

1. Add RichTextLabel
2. Enable BBCode
3. Enter this to the text field:

[rainbow freq=0.3 sat=1 val=1]This is an example text.[/rainbow]
[rainbow freq=-0.3 sat=1 val=1]This is an example text.[/rainbow]
[rainbow freq=0 sat=1 val=1]This is an example text.[/rainbow]

Minimal reproduction project

rainbow_issue.zip