We have been finding many of that by the pounds. Unless it shows a true blue in the sunlight, it wouldn't be classified as a "blue;" but instead, it would be known as a "smoke" in reference to the smoky gray colors by local hunters. There has in fact been E. Blues found in that region, they are a little more tricky to find. We go there many times a year, even finding quartz geodes. All in all, it kinda does look like one, but if it shows a true blue color in the sun, then it is one. Most agate in this region are more smoky blue-gray to a slate gray in color. Which are not Ellensburg Blue agates.
My conclusion: It looks more like a smoke, not strong enough blue tone to be classified as an authentic Ellensburg Blue. It is a nice specimen with the beautiful striations, that particular find is a good one.