Installing custom advancements datapacks will no render the real format/color in the advancement descriptions. E.g.: With Blaze and Cave's Advancement Pack, a datapack that changes the goals and challenges description color, just goal descriptions respect the custom color (light blue), but challenge and even tasks change their descriprtion color to light gray, wich make the advancement gui a little bit bored in comaprision with vanilla one (in this specific case).