Yes the black theme just uses the default link color since it’s already black. You can add this to your css in the black section if you want (or you could add it in your own custom section) –
.epik-black a {
color: #000;
}
You can change that color to whatever you need. If you want it to look bolder then you could add font-weight
like this –
.epik-black a {
color: #000;
font-weight: 700;
}