Turuncu, pembe, mor ve sarı şemsiyeler kumsalı renklendiriyor.

In Turkish, adjectives never inflect for number or case—they remain exactly the same whether the noun is singular or plural. Only the noun itself takes the plural suffix (-ler/-lar).
• şemsiye (umbrella) → şemsiyeler (umbrellas)
• kırmızı arabalar (red cars), not kırmızılar arabalar

That -ı is the 3rd-person singular accusative suffix, marking kumsal (“beach”) as a definite direct object (“the beach”).
• kumsal = “a beach” (indefinite, unmarked)
• kumsalı = “the beach” (definite, accusative)

Turkish has a basic Subject-Object-Verb (SOV) word order. Here you see:
1) Subject = şemsiyeler
2) Object = kumsalı
3) Verb = renklendiriyor (“is coloring”)

Breakdown of renklendiriyor (“is coloring”):
1) renk – noun root “color”
2) -lendir – causative suffix “cause to be X” → “to color”
3) -iyor – present-continuous suffix “is …ing”
Altogether: renk + -lendir + -iyor = “(he/she/it) is coloring”

In Turkish, the absence of a personal suffix after the tense/aspect marker indicates 3rd-person singular. Other persons use:
• -yorum (I …)
• -yorsun (you …)
• -yoruz (we …)
etc.
Here renklendiriyor = “he/she/it is coloring.”

Turkish has no independent articles. Indefiniteness is unmarked (zero article), while definiteness is shown by the accusative suffix (-ı/-i/-u/-ü). E.g.:
• kedi = “a cat” (indefinite)
• kediyi = “the cat” (definite, accusative)

Suffix vowels harmonize with the last vowel of the stem:
• şemsiye ends in i (front unrounded) → plural suffix is -ler → şemsiyeler
• kumsal ends in a (back unrounded) → accusative is -ı → kumsalı