Ion Button custom colors

I’m trying to set dynamic colors for the background-color and color of an ion-button.
What I’ve achieved so far:

My problem: The button color overlays the button outline.
Is this an Ionic issue, how can I get around this?

My code:


<ion-button *ngFor="let d of districts" shape="round"

Method in my Component:

getDistrictStyle(district: District) {
        if (district) {
            const colors = this.colorGenerator.getDistrictColors(district);
            return {
                'background-color': colors[0],
                'color': colors[1]

getDistrictColors(district: District) simply returns an array with two colors in hex (red and white in this case).