Table styling different background colors per heading column

You can use the CSS nth-child selector to achive this:

.main_color tr.avia-heading-row th:nth-child(1) {
    background: red;
}
.main_color tr.avia-heading-row th:nth-child(2) {
    background: yellow;
}
.main_color tr.avia-heading-row th:nth-child(3) {
    background: green;
}

Then you can just change the CSS declaration to tables with ‘Alternate Content’ styling:

.alternate_color tr.avia-heading-row th:nth-child(1) {
    background: red;
}
.alternate_color tr.avia-heading-row th:nth-child(2) {
    background: yellow;
}
.alternate_color tr.avia-heading-row th:nth-child(3) {
    background: green;
}

or use a more general declaration for all tables:

tr.avia-heading-row th:nth-child(1) {
    background: red;
}
tr.avia-heading-row th:nth-child(2) {
    background: yellow;
}
tr.avia-heading-row th:nth-child(3) {
    background: green;
}

if you want to change it only in a specific area of the site add a custom CSS class to the mother layout element:
=> https://kriesi.at/documentation/enfold/add-custom-css/#enable-custom-css-class-name-support

.my-special-area tr.avia-heading-row th:nth-child(1) {
    background: red;
}
.my-special-area tr.avia-heading-row th:nth-child(2) {
    background: yellow;
}
.my-special-area tr.avia-heading-row th:nth-child(3) {
    background: green;
}

If you want help, you need to be more specific about what you tried, what’s not working. Or at least share a link to your current site.
There are now three working examples which are tested and proofed on an Enfold-installation and you just write “does not work” …

Ok … as i can’t see the private content i can’t help you any further.