A nice example of polymorphism in Angular! You could also get rid of the if statements entirely and use a switch statement.

Or if such trivial functionality doesn’t warrant creating multiple sub-class services, I like to use a Map and keep it all in one Service.

public typeColors<Map<string, string>> = new Map<string, string>([
    ['math', 'red'], 
    ['eng', 'blue'] ...

getColor(type: string): string {
    return this.typeColors.get(type);
}