Ester

Already thought about changing your RSS reader as well as changing your writing style, perhaps?
You could give us at least a little more information, e.g. which one use and so on…

Take a look at this, it might help you:
https://codex.www.ads-software.com/Changing_File_Permissions

By the way, it’s called chmod, not chomd

Well, I created a small example, tested in most browsers:
https://www.seeder.de/rainbow.htm

You asked if it should be under #header. I haven’t found such an id on your Homepage but you should understand how to do it by looking at that source code.

By the way this method only works if the affected words always have the same amount of letters.

It was done with javascript.
<script type="text/javascript" src="https://www.blinklist.com/HandySolo/cloud.js&logo=0&title=Most popular BlinkList Tags&fontsize=10&cloudsize=100&fontcolor=23598C&colorbegin=409FCF&colorend=FF6600"></script>

You might also try following method if you know the color-codes:
<span>H<span>E<span>L<span>L<span>O</span></span></span></span></span>

with this stylesheet

span {color:black}
span span {color:darkgrey}
span span span {color:grey}
span span span span {color:lightgrey}
span span span span span {color:white}

(Why this way and not an end-tag after each letter? Then you don’t have to specify an id to each span-tag what results in a cleaner html code itself but messes up the css a bit)