UnityGame/Library/PackageCache/com.unity.ugui/Documentation~/TextMeshPro/RichTextOpacity.md

Text Opacity (Alpha)

Use the <alpha> tag to change text opacity. It works with hexadecimal values.

Example:

<alpha=#FF>FF <alpha=#CC>CC <alpha=#AA>AA <alpha=#88>88 <alpha=#66>66 <alpha=#44>44 <alpha=#22>22 <alpha=#00>00

Successive <alpha> tags