1. Go to Packages/Color Scheme – Default.

2. Open the file [theme-name].tmTheme.

3. Find the syntax element among the <key> tags.

4. Change the color in the <string> tag.

5. Examples:

lineHighlight – set current line background in the next <string> attribute
Function name – set function name foreground in programming languages (JavaScript, PHP, Java) in the <string> tag under the “foreground” <key> tag.
Comment – comments color, the same <string> under “foreground” <key>.