Change Page color

You should do this in a child theme not the original theme.
the rule for back ground color is

#content{
background: none repeat scroll 0% 0% rgba(182, 182, 182, 0.8);}

the rgb in the command stands for red green blue and the 0.8 is the alpha level or how transparent the color is. the values run from 0 to 1 where 0 is invisible and 1 is solid.

there an rgb color picker on this page
https://www.rapidtables.com/web/color/RGB_Color.htm

the link colors are set with this rule

#primary-main h2.entry-title a {

    color:<<color>>;

}

you just need to replace the color with the one of your choice

here a color picker you can get the value from.
https://www.w3schools.com/tags/ref_colorpicker.asp

Note this color is rgb but it is in hex numbers unlike the rgba command in the background color. Just use the values that start with the pound sound on the colorpicker site.

Here a tutorial on the css commands
https://www.w3schools.com/cssref/css_colors_legal.asp

Hey, I didnt get a result using the methods above, but i did manage to change the page colour from grey to one of my choice by editing the default.css at line 580.

I downloaded the file via ftp, and then (after renaming the original as a backup), changed the reference to grey at line 580 and then uploaded the modified default.css

The file can be found in wp-content/themes/fifteen/css/skins

hope this helps ??