The greenish flower buds open into large balls of white, pink or blue blooms, according to the particular variety.
For some cultvats, the colour of the flower depends on the acidity of the potting soil. Blue-flowered varieties like 'Nikko Blue', 'All Summer Beauty', 'Mariesii', 'Perfecta Blue' and 'Endless Summer' need acidic soil (pH of 5.0 to 5.5) to stay blue. Otherwise, if the soil is neutral or alkaline (pH 6,0 à 6,5), they will turn bluish-pink. If you wish to acidify the soil, you can buy various products containing sulphur, iron sulphate or aluminum sulphate from a gardening centre.
The white-flowered cultivars ('Maculata', 'Lanarth', 'Sister Therese', 'Vetchii') are not affected by soil acidity and those with pink flowers ('Bouquet Rose', 'Forever Pink', 'Pink Beauty', 'Masja') do not turn completely blue in acidic soil, but acquire a purple tint.
There are also cultivars with very decorative variegated foliage (‘Light O Day,’ ‘Lemon Wave,’ ‘Maculata,’ ‘Tricolor’).