IME, it depends on the heuch :-) Dark purple or deeply colored ones, including the coppers, bronzes and orange, retain their color better in more sun than shade; chartreuse, lime or yellow/gold leaved cultivars prefer more shade. Green leaved forms will tolerate either. But all prefer an organically rich soil, well drained but moisture retentive. If you give them the soil conditions they like, most are very tolerant about quite a lot of sun.