Ben duvarı sarıya boyuyorum.

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Breakdown of Ben duvarı sarıya boyuyorum.

• duvar: the wall
• -ya: to
• -ı: accusative

Questions & Answers about Ben duvarı sarıya boyuyorum.

Why does duvarı end in -ı rather than just duvar?

The -ı is the accusative case marker, showing that duvar (“the wall”) is the direct object of the action “paint.” In Turkish, definite direct objects almost always take the accusative suffix ( -i/–ı/–u/–ü ) following vowel harmony:
• duvar → duvar-ı
This tells the listener which specific wall you’re painting.

Why is sarı changed to sarıya instead of just using sarı?

Color words act like targets in painting verbs, so they go into the dative case (“to yellow”). The suffix for dative is -a/–e (again, vowel harmony). Thus:
• sarı → sarı-ya
This expresses “(I’m painting the wall) to yellow,” i.e. “I'm making it yellow.”

What is the little y in sarıya for?

That y is a buffer consonant. When you attach a vowel-initial suffix (-a/–e, here -ya) to a stem ending in a vowel, Turkish inserts y to avoid two vowels running together:
• sarı + -a → sarı-ya

Why is the verb boyamak conjugated as boyuyorum here?