Set gui default text color

[friendlyhj]

Adds a way to change actual color when font render draws color in #404040 color. It is helpful for dark mode texture pack.

[what-the-diff]

PR Summary

• New Configuration Option for GUI Text Color
  A new feature has been added that allows users to customize the color of the text in the Graphical User Interface (GUI). This is done by setting a hexadecimal RGB color code in the configuration file.

• GUI Text Color Implementation
  We have included a procedure in our software loading logic that applies the user's custom text color during startup, unless the standard text color of "404040" is already set.

• GUI Text Color Application Mechanism
  A new system component (Mixin class in programming terminology), responsible for altering the font color according to the user specification, has been created for efficient implementation of the new feature.

• Registration of New Mixin
  In order for the system to recognize and effectively utilize the new text color alteration component, we have registered it in our system's Mixin registration file.