I agree, better to have some amber and the whole plant ripe, rather than loads of clear ones. As you start to see amber, you will notice less and less clear ones. I have never seen the whole plant show 100% milky, I always get a mix. Most of the clear trichomes are gone at about 10% to 20% amber on my White Widow. The purple I grew was hard to tell, I had to just wait for the clear ones to turn to milk on most the bud before harvest because it was very hard to tell what was amber (could be my jewelers loupe).
Some folks here freak out when you tell other growers to wait for amber, but it's a great sign of ripeness. Something you can't find in a science paper.