How to change H1 font, color and size in Joomla
Depending on the theme (template) used, go and open to edit templates/your_template_name/css/template.css, according to the picture.
Depending on the font size, type, and color you want, at the end of the table try to type the following:
The example is considered for black letters, as well as without this line color can still remain black. For another font color, just type in the color code. It may doesn't work on all templates.