Pronounced as one letter, - go through all the letters if the alphabet
And written with three, - made with three letters
Two letters there are, - two letters are the same
And two only in me. - what do you have two of?
I'm double, I'm single, - two of it, and one of it...
I'm black, blue, and grey, - colours of what???
I'm read from both ends, - what is read with???
And the same either way. - are the same...
i hope this helps without giving away the answer...