Rule 1: 1. Colours: أَسْوَدُ، أَبْيَضُ and their feminines
The basic colours are adjectives of the pattern أَفْعَلُ: أَسْوَدُ black, أَبْيَضُ white, أَحْمَرُ red, أَخْضَرُ green, أَصْفَرُ yellow, أَزْرَقُ blue. They take no tanwīn: قَمِيصٌ أَبْيَضُ, رَأَيْتُ قَمِيصًا أَبْيَضَ. Their feminine is فَعْلَاءُ: سَوْدَاءُ, بَيْضَاءُ, حَمْرَاءُ, خَضْرَاءُ, also without tanwīn. Since plurals of things are feminine singular, a plural of things takes the فَعْلَاءُ form: أَقْمِشَةٌ بَيْضَاءُ white cloths.
اَلْقَمِيصُ أَبْيَضُ وَالْحِذَاءُ أَسْوَدُ.
al-qamīṣu abyaḍu wa-l-ḥidhāʾu aswadu
The shirt is white and the shoe is black.
اِشْتَرَيْتُ قُمَاشًا أَحْمَرَ.
ishtaraytu qumāshan aḥmara
I bought a red cloth.
Accusative with fatḥa, no tanwīn.
هٰذِهِ الْمَائِدَةُ سَوْدَاءُ.
hādhihi-l-māʾidatu sawdāʾu
This table is black.
Feminine singular فَعْلَاءُ.
اَلْأَكْيَاسُ خَضْرَاءُ وَالصَّنَادِيقُ بَيْضَاءُ.
al-akyāsu khaḍrāʾu wa-ṣ-ṣanādīqu bayḍāʾu
The bags are green and the boxes are white.
Plurals of things: feminine singular colour.