According to two sources I found the answer is red. I actually thought that seemed strange and started looking into it when I saw this question here unanswered.
I found this in Michael Prestwich's book, "Knight."
"...a red cloak is worn to show humility."
A list of Catholic church associations of colors lists humility being among the ideas conveyed by red. Knighthood and Catholicism being closely linked, it is not surprising they share color symbolism.
I suppose the ideas on what color symbolizes humility has probably changed through history as I have also found mention of white and gray being the color of humility.
The color white is often associated with humility. It represents purity, simplicity, and modesty.
The color that is often associated with humility is brown. Brown is seen as a grounded and stable color, symbolizing simplicity and sincerity. It is often used to convey a sense of humility and down-to-earth nature.
a dead looking camomile
A lotus flower is often seen as a symbol of humility in many cultures. Its ability to grow from murky waters and rise above the surface to bloom in beauty represents the idea of purity and humility in the face of adversity.
the color that represents to be organised is white
Pink. That's the color that represents their party.
The color that often represents the past is sepia.
Blue Is the colour that represents the word believe
Blue represents trustworthy
West African Wisdom: Adinkra Symbols & MeaningsDWENNIMMEN - "ram's horns" - humility and strength
Deep orange represents pride.
There is no universally agreed-upon color that represents laughter. However, in the field of color psychology, yellow is often associated with happiness and joy, emotions that are often expressed through laughter. Yellow is considered a warm and cheerful color that can evoke feelings of positivity and energy, making it a potential candidate to represent laughter in a symbolic context.