How can I add a color to the top section of the table

Hi therem

you can use some CSS to change all Block Tables:

.wp-block-table thead tr {
    background-color: #f00;
    color: #fff;
}

If you want it to ONLY affect specific styles then select the table and in Advanced > Additional CSS Class(es) add a custom class eg. table-style-red

Then use this CSS:

.table-style-red.wp-block-table thead tr {
    background-color: #f00;
    color: #fff;
}