الأحمر

In a sentence

• السيارة الحمراء تسير بسرعة.

  The red car is moving fast.

  Here, 'الحمراء' is an adjective in the feminine form describing the noun 'السيارة' (car), which is feminine in Arabic.

• الشمس حمراء عند الغروب.

  The sun is red during sunset.

  In this sentence, 'حمراء' is used as a predicate adjective describing the state of the subject 'الشمس' (the sun), agreeing in gender.

• أحب اللون الأحمر الجميل.

  I love the beautiful red color.

  Here, 'الأحمر' is a noun referring to the color red, in the definite form (the red), showing a general concept.