For Sikhism, colours are strong depictions of mental state. There is no physical relevance to colours. A Sikh is expected to wear ordinary clothes that do not attract attention. Neither is playing with colours encouraged.
A key ingredient used during holi is called Gulal. Its a deep red coloured powder which is used to colour others. The Guru says this about Gulal:
ਚੀਤਿ ਆਵੈ ਤਾਂ ਰੰਗਿ ਗੁਲਾਲ ॥
When my mind is attached to Him, I am dyed in the deep crimson of His Love.
In the daily Sikh prayer, the first reference to the word colour appears in Japuji Sahib.
ਭਰੀਐ ਮਤਿ ਪਾਪਾ ਕੈ ਸੰਗਿ ॥
But when the intellect is stained and polluted by sins committed by us,
ਓਹੁ ਧੋਪੈ ਨਾਵੈ ਕੈ ਰੰਗਿ ॥
it can only be cleansed by the colour (Love) of His Name.
Sri Guru Granth Sahib recognises two colours: Kusumbh and Majith. Kusumbh is light orange in colour, while Majith is dark red, even crimson. Kusumbh is the color of a flower (Butea monosperma) called “flame of the forest” (called FF henceforth in this post). When its immersed in water for a few hours, the flower looses its colour, and the water becomes coloured.
When Guru Nanak was visiting Mecca, he was asked whether Hinduism was the greater religion or Islam. His reply was as under:
ਕਚਾ ਰੰਗੁ ਕਸੁੰਭ ਦਾ ਪਾਣੀ ਧੋਤੈ ਥਿਰ ਨ ਰਹੋਈ।
As the colour of FF flower is impermanent and is washed away in water, likewise the colours of religiosity are also temporary.
To the contrary, majith is permanent. Its effects are not physical, rather its colouring is for the soul:
ਮਨਮੁਖੁ ਰੰਗੁ ਕਸੁੰਭੁ ਹੈ ਕਚੂਆ ਜਿਉ ਕੁਸਮ ਚਾਰਿ ਦਿਨ ਚਾਗਾ ॥
The self-willed manmukh is like the false color of the FF flower, which fades away; its color lasts for only a few days.
ਖਿਨ ਮਹਿ ਬਿਨਸਿ ਜਾਇ ਪਰਤਾਪੈ ਡੰਡੁ ਧਰਮ ਰਾਇ ਕਾ ਲਾਗਾ ॥੨॥
He perishes in an instant; he is tormented, and punished by the Righteous Judge of Dharma. ||2||
ਸਤਸੰਗਤਿ ਪ੍ਰੀਤਿ ਸਾਧ ਅਤਿ ਗੂੜੀ ਜਿਉ ਰੰਗੁ ਮਜੀਠ ਬਹੁ ਲਾਗਾ ॥
The Lord’s Love, found in the Sat Sangat, the True Congregation, is absolutely permanent, and colorfast.
ਕਾਇਆ ਕਾਪਰੁ ਚੀਰ ਬਹੁ ਫਾਰੇ ਹਰਿ ਰੰਗੁ ਨ ਲਹੈ ਸਭਾਗਾ ॥੩॥
The cloth of the body may be torn to shreds, but still, this beautiful color of the Lord’s Love does not fade away. ||3||
ਹਰਿ ਚਾਰ੍ਹਿਓ ਰੰਗੁ ਮਿਲੈ ਗੁਰੁ ਸੋਭਾ ਹਰਿ ਰੰਗਿ ਚਲੂਲੈ ਰਾਂਗਾ ॥
Meeting with the Blessed Guru, one is dyed in the color of the Lord’s Love, imbued with this deep crimson color.
So how does the Guru celebrate Holi. The answer is obvious:
ਹੋਲੀ ਕੀਨੀ ਸੰਤ ਸੇਵ ॥
Holī kīnī sanṯ sev.
I celebrate the festival of Holi by serving the Saints.
ਰੰਗੁ ਲਾਗਾ ਅਤਿ ਲਾਲ ਦੇਵ ॥੨॥
Rang lāgā aṯ lāl ḏev. ||2||
I am imbued with the deep crimson color of the Lord’s Divine Love. ||2|
Finally I want to share another related hymn:
ਲਾਲ ਰੰਗੁ ਤਿਸ ਕਉ ਲਗਾ ਜਿਸ ਕੇ ਵਡਭਾਗਾ ॥
One is dyed in the (red) color of the Lord’s Love, by great good fortune.
ਮੈਲਾ ਕਦੇ ਨ ਹੋਵਈ ਨਹ ਲਾਗੈ ਦਾਗਾ ॥੧॥
This color is never muddied; no stain ever sticks to it. ||1||
ਪ੍ਰਭੁ ਪਾਇਆ ਸੁਖਦਾਈਆ ਮਿਲਿਆ ਸੁਖ ਭਾਇ ॥
He finds God, the Giver of peace, with feelings of joy.
ਸਹਜਿ ਸਮਾਨਾ ਭੀਤਰੇ ਛੋਡਿਆ ਨਹ ਜਾਇ ॥੧॥ ਰਹਾਉ ॥
The Celestial Lord blends into his soul, and he can never leave Him. ||1||Pause||
ਜਰਾ ਮਰਾ ਨਹ ਵਿਆਪਈ ਫਿਰਿ ਦੂਖੁ ਨ ਪਾਇਆ ॥
Old age and death cannot touch him, and he shall not suffer pain again.
ਪੀ ਅੰਮ੍ਰਿਤੁ ਆਘਾਨਿਆ ਗੁਰਿ ਅਮਰੁ ਕਰਾਇਆ ॥੨॥
Drinking in the Ambrosial Nectar, he is satisfied; the Guru makes him immortal. ||2||