Do you mean the 青(blue) can also mean green thing? But Kogasa's clearly saying 緑(green)...
In Japanese and (maybe) certain other Eastern languages, the word for "blue" is the same as the word for "green." This leads some people to sometimes choose the wrong color when one or the other is correct. Just look at pictures of Hatsune Miku and you'll see her hair color all over the place - green hair, aqua hair, blue hair, and everything in between. The same goes for her eyes, though at least most artists have the consistency to match them to her hair. To make it clear, the correct colors for Hatsune Miku are aqua hair and aqua eyes - almost if not exactly the same color as Kogasa's hair in the 4koma on the right.
In Japanese and (maybe) certain other Eastern languages, the word for "blue" is the same as the word for "green." This leads some people to sometimes choose the wrong color when one or the other is correct. Just look at pictures of Hatsune Miku and you'll see her hair color all over the place - green hair, aqua hair, blue hair, and everything in between. The same goes for her eyes, though at least most artists have the consistency to match them to her hair. To make it clear, the correct colors for Hatsune Miku are aqua hair and aqua eyes - almost if not exactly the same color as Kogasa's hair in the 4koma on the right.
This is true for 青 (ao), but the specific word used here is 緑 (midori), which unambiguously refers to a lush, verdant green. This was TwinLeadersX's point.
I believe this is probably just a set-up to a red-green color blindness joke (the green here is also referred to as midori and not ao). Karaagetarou has drawn Kogasa before with blue/aqua eyes.
The blue/green lens of anaglyph 3-D glasses has been variously described as either ao or midori, so it can't be just a set-up for the 3-D glasses joke alone.
Ah! I can even see the pebbles in the road!Which can you see better using your right eye?
Te Wi
U Do
N Ge
Tewi Udonge, written right to left on the boardCats cry "meow", don't they?In that case...And your left eye?Raison d'Etre NazrinGreen!They do. Why?Hmmm? What's wrong, Chen?you cry "meow", don't you?Eh!?Stp
StpHmmm...farsighted and nearsighted?? That's a bit troublesome.Let's try a special prescription.Corrected Kogasa-chanRed!Y-...yeah.TurnWant some tea?