I believe it is "incomplete (or intermediate) dominance."
I found this by searching Google under the key words "gene pair blend" to get these possible sources:
(Broken Link Removed)
Use the <Find> command to search for "blend" within the sites.
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.
I hope this helps. Thanks for asking.