I've not found any candle color that is specific to mothers, however, white candles are universal and are often used in place of another color when need be. Perhaps you too could use a white candle for your ritual. However, I've also provided a list of candle colors and their correspondences so that you may make your own decision on the matter. I do hope this helps you dear.
The following list was obtained from either "Wicca" or Living Wicca" by Scoot Cunningham. I can't quite remember which book it was, but I've read both and I believe they both have information on candle colors.
White: Protection, purification, peace, truth, and sincerity. (can also be used in place of another color, as it is a combination of all colors.)
Red: Protection, strength, health, vigor, lust, sex, passion,
Black: Absorbing and destroying negativity, healing diseases,
Light Blue: Tranquility, healing, patience, happiness.
Dark Blue: Change, flexibility, the subconscious mind, psychic
work, and healing.
Green: Finances, money, fertility, prosperity, growth, luck, and
Yellow: Intellect, attraction, study, persuasion, confidence, and
Brown: Working magic for animals, healing animals, and the home.
Pink: Love, honor, and friendship.
Orange: Adaptability, stimulation, and attraction.
Purple: Power, healing diseases, spirituality, and meditation.
Blessed Be and With Respect,