Ben duvarı sarıya boyuyorum.

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Breakdown of Ben duvarı sarıya boyuyorum.

• duvar: the wall
• -ya: to
• -ı: accusative
• sarı: yellow
• boyamak: to paint

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?

boyuyorum is the first-person singular, present continuous form of boyamak (“to paint”):

1. Stem (drop -mak): boya-
2. Continuous marker: -yor (be-…ing)
3. Person/number: -um (I)
   So you get boyuyor-um, and vowel harmony turns o → u: boyuyorum. It means “I am painting.”

Is Ben necessary at the beginning of the sentence?

No. Turkish is a pro-drop language, so the subject pronoun ben (“I”) is optional when the verb ending (-um here) makes the subject clear. Both of these are correct:
• Ben duvarı sarıya boyuyorum.
• Duvarı sarıya boyuyorum.

How would I say “I painted the wall yellow” instead of “I am painting”?

Switch the verb to the simple past (perfective) tense by using -dı/–di plus the person ending. You get:
• boya- + -dı → boyadı
• boyadı + m → boyadım
Full sentence:
• Ben duvarı sarıya boyadım.
“I painted the wall yellow.”

Could I express the same idea with the passive voice?

Yes. The passive of boyamak is boyanmak (“to be painted”). In present continuous passive:
• Duvar sarıya boyanıyor.
Here duvar is the subject, sarıya remains the target color in dative, and boyanıyor means “is being painted.” This shifts focus away from who is doing the painting.

If I want to ask “What color are you painting the wall?”, how do I form that question?

You use the question word for colors and the dative case:
• Duvarı ne renge boyuyorsun?
Literally: “Wall-ACC what color-DAT are you painting?”
Answer: Duvarı sarıya boyuyorum.

Can boyamak be used with things other than walls, say hair or furniture?

Absolutely. boyamak works with any paintable object. Just put the object in the accusative and the color in the dative:
• Saçımı maviye boyadım. (“I dyed my hair blue.”)
• Masayı beyaza boyuyorum. (“I’m painting the table white.”)

How do I form the negative of boyuyorum?

Insert the negation marker -ma-/-me- before the continuous marker -yor-:
• boya- + -ma + -yor + -um → boyamıyorum
Sentence: Duvarı sarıya boyamıyorum. (“I am not painting the wall yellow.”)