Why is it not "yw'R"? In English we say, "What is THE colour of his eyes?" Am I misunderstanding the grammar? Thank you.
In a noun + noun construction, the first noun is definite by construction and doesn't need (and cannot take) an additional article.
Basically, you can translate something like "A B" as "the A of B"
Here, you have "lliw" + "ei lygaid e", so "color" + "his eyes" becomes "the + colour + of + his eyes".
"y lliw ei lygaid e" is as grammatical in Welsh as "the my mother's hat" or "my mother's the hat" would be in English -- there, too, "hat" is definite by virtue of the possessive construction and can't take another definite article.
The second noun can have an article (lliw'r llygaid "the colour of the eyes" -- then you have "the + colour + of + the eyes", which is fine), but not the first. (To compare it with English possessive, "the teacher's son" is fine with a "the" belonging to the owner, "the teacher".)
Is it possible to use pa instead of beth , i.e. Pa yw lliw ei lygaid e?
Or must pa be followed by a noun, i.e. Pa liew yw ei lygaid e?
- Pa liw [yw/ydy] ei lygaid?
(Beth...? in this context is actually derived from the now little used Pa beth...?)