Is it possible to format a calendar view of a list in modern, with hex codes instead of the sp-css colours?

I'm trying to format a calendar view of a list (generated from the event itinerary template) using custom hex code colours instead of the sp-css colours. I've used the hex codes successfully in the list view column formatting but just can't get it to work in the calendar view. I want the colour coding to match in both the list view column and the calendar view.

Here's the JSON generated by the calendar view formatting designer:

Rule 1: Show all items as yellow

Rule 2: If category column (Eventtype) is equal to 'SRF', show as blue

If I wanted to swap the sp-css-backgroundColor-BgCornflowerBlue to hex code #1C46C0 instead - any ideas how to do this please? It's stumped Copilot as well.

Thanks in advance.

{

"$schema": "https://developer.microsoft.com/json-schemas/sp/v2/row-formatting.schema.json",

"additionalEventClass": {

"operator": ":",

"operands": [

{

"operator": "==",

"operands": [

"[$Eventtype]",

"SRF"

]

},

"=if(@isSelected == true, 'sp-css-color-WhiteFont sp-css-backgroundColor-BgBlue' , 'sp-css-backgroundColor-BgCornflowerBlue sp-css-color-CornflowerBlueFont')+' sp-field-fontSizeSmall'",

"=if(@isSelected == true, 'sp-css-color-WhiteFont sp-css-backgroundColor-BgBrown' , 'sp-css-backgroundColor-BgGold sp-css-color-GoldFont')"

]

}

}