Transparent and WHAT?

My IQ is152 (that's supposed to be 'genius', but read on): I'm afraid that this simple little question has me most perplexed.

My teacher gave me four sandwich baggies and asked me to describe each one in two words. The first 3 were easy:

1) transparent and red,

2) transparent and yellow,

3) transparent and blue,

but I'm having trouble with the fourth one. I said,

'It's transparent and it has no colour.'

Teech said, '"It has no colour" is 4 words, not 1. You score 75%.'

I asked whether the 1 word he wanted was an English word. He said,''I COULD be... or it might be LATIN (classical or ecclesiastical) -- or a LATINATE language (Italian, Spanish or French) -- or GREEK (modern or classical). Come on; don't overthink it; it's EASY!'

So, Teech says if I'm going to cheat and fall back on Yahoo! Answers, the first correct response will get 100% for its author, and I'll be stuck with my 75%.

WHAT, PLEASE, IS A ONE-WORD ADJECTIVE MEANING 'HAS NO COLOUR'? (Oopsie, didn't mean to shout: Please forgive, but this is REALLY driving me crazy!)