In this update, I added 1 placeholder. (So far 1, in the future there will be more).

With this placeholder, you can create gradient labels wherever PlaceholderAPI 2.9.2 is supported.

Using:
%ac_gradient_ffffff, 000000_0.8_gradient text!%

Where
ffffff, 000000 - are the colors separated by commas
0.8 - the degree of confluence
gradiented text! - the text to which the gradient will be applied