nth-of-type miscounting

[marama]

Hello. Having some trouble with the counting of entries and the nth-of-type pseudo-selector. I wanted to alternate the background colour of the entries and tried to use this:

div#entries > div.inner > div.entry-wrapper:nth-of-type(odd)
{ background-color: #35bf9d; } /*blue*/

div#entries > div.inner > div.entry-wrapper:nth-of-type(even)
{ background-color: #525dbf; } /*green*/

But instead of the blue colour being behind the first post, it's behind the second and the green is behind the first, basically swapping the colours opposite from the code. I played around with different formulas and what seems to be happening is the first entry is being counted as the second type, with the last counted as 21 instead of 20. So at this point, I'm lost. I know if I was doing a simple alternating pattern, I could just switch the colours and be done, but I was planning to use different equations to vary it, but with the odd counting, I can't be sure if the equations will work right now.

Any help is greatly appreciated. Thank you.