Today I drove past a street vendor, wife says stop look at the nice looking mangoes, they were large and green, I figured they were keitts, which is probably the most readily available down here.
I told my wife to leave me one in the bag she thought was ripe, and on my way to work later, I could smell the nice mango aroma. I said to myself, this cannot be a Keitt.
it was only slightly yellow on one part, rest was all green. cut it open, and it was ripe, after tasting I realized for sure it was a Kent.
anyway, yes they can be all green and ripe, slight give and aroma, should tell you when they are ready.