This guide explains complication slot editing.
As complication layout on the right of wfs when selected does not mean u are choosing that specific layout its just a preview of what would look like if a complication is using that layout. Most complication can have more than one layout it can use. If you have more than one on the right list, the complication will choose a default from the list.
Saying that
To be able to change the Font, size and Color and force a layout for the complication.
you need to either select every one of the layout and change the Font,size and color or edit each element in each of the layout (you can hide elements too).
or remove layouts that you don;t want the complication to use , leaving what you think the complication can use (e.g its own default)
To remove
mouse over to show the “X” then click the "X’
for this example I left only one layout - weather default layout (removed all the others)
On the gw 5 pro watch not wfs preview
P.s if u go by removing the other templates. When users try to customise the complication they were notice some missing complication from the list. Because some of the complication doesnt recognised your selected template.