Table: Conditional header colors

[Breezy]

[Qlik Sense]

Hi, I am trying to change the header colors based on what is selected. I have ten letters to select from.

I have my code:

=if(count([Letter]) > 9, rgb(17,30,108),rgb(128,0,128))

I assume this code goes in the "Appearance" section but I'm not sure where. Currently, my table colors are correct UNLESS I choose more than one letter. In the example below, I want purple. Unfortunately, if I pick multiple letters at once, it actually shows up as blue. How can I resolve this?