text foreground color

I want to change foregrond color texts in posts to black

You’d need to post a link to your site.

My site is https://www.primeirapaginaseo.com.br/

Not sure if this is what you mean, but let’s give it a try.

In your CSS, search for:

.index p {
color: #868686;
font: normal 12px/1.8em "Liberation sans", Arial, Helvetica, sans-serif;
}

Change the value of the #868686.

I’m sorry but as you are using a commercial theme, you need to seek support from the theme’s vendors.
https://www.templatesold.com

Xaliber, i changed that value, but did not took effect. It remains the same color from original theme (gray).