Can horse chestnuts help the appearance of varicose veins?

NO! Horse chestnuts are poisonous! There are some claims that an extract of horse chestnut may be helpful for varicose veins, but the evidence is weak at best.
Varicose Veins. Horse chestnut extract put into a tablet form has been demonstrated (in well-done medical studies) to help with some of the swelling and discomfort symptoms associated with varicose vein disease. But unfortunately it does not cure the disease, prevent disease recurrence or spreading of the disease, or help with the appearance of the veins. See a vein specialist for actual treatment.
No. Horse chestnut can help the symptoms you might have from your varicose veins, especialy swelling, but it won't do anything to help the appearance of the veins.
Vein evaluation. There is no medical evidence to document that horse chestnut will improve the appearance of varicose veins. Homeopathic supplements such as horse chestnut, escin, diosmin and bioflavonoids are just that-supplements. They are not 1st line treatment for varicose veins. It would be prudent for you to have a venous evaluation by a vein specialist.