To make the change in main theme
1. You open wpresidence/css/css-images/unit.png in an editor. Theme default images are also in theme pack.
2. You change image color with the editor
3. You save with the same name and extension on your computer
4. you upload via FTP and overwrite the default image.
For other images you need to look for the name, the above instructions are only for featured images.
To make the change in child theme
Original images can be taken from demo content folder, pins and other png folder
You edit them with a vector editor program, like Fireworks and add the colors you wish.
In the theme, the images are in css/css-images folder
Create the same folder in child theme
Add the images in child theme folder
And change CSS in child theme to new image path
Ex for compare icon: (if you use demo pack child theme), after you create the images folder, you add your new images in there and in style.css you change the img path for compare class to your child theme path.
So css should look like in this text document
Urls should be adapted to your url path.