You don't actually burn more endurance, but end red enhancements are subject to Enhancement Diversification - a general system which reduces the benefit of trying to slot any attribute to a high level.
Mids indicates you're entering the "maximum penalty" area of ED by colouring numbers red; that doesn't indicate that anything's wrong, just that you won't gain much if you try to slotting an attribute any further.
thank you for the quick response!!! 
i was getting really confused with it all
yw - happy Midding!
i have a question about mids and extra endurance burn in general, am i right in thinking that you burn more endurance if you slot more than 3 of the same enhancements or go over 100% e.g having 4 dmg slotted in a skill takes you over 100 which makes you burn more endurance than normal?, now the problem i am having with mids is that for example i am putting in 3 end red into a skill it states 99.08% for end red, there is only 3 of said slotted enhancement but the value on mids is coming up red???