Turtle special island

So how does this work??

I know that it spawns for 30 minutes, twice a day on mondays, but how do we know which turtle is coming?
for example, today i got rush of the black turtle on the 2nd run, but i was rly hoping to get red and green. 
it was my first time doing the turtle island so i assumed it would be mixed, but is it always just one type of turtle?
does this mean i have to wait till next monday to hopefully get a different colored turtle??

Thanks

hi 
for now we have black/purple turtle time only.
We will get different coloured turtles too but nobody knows
when it will be.

o wow, thats disappointing. has that been the case for a while now?
does that mean i just have to use black turtles to level up other classes?

yes since the beginning only purple 
just use the turtles on anybody i know it feels like you waste them
but thats it
well there  are sometimes events with colored turtles but they are only limited. since the japanese version has different colored turtle time we will get them too we just have to wait

alright thanks