Colors.—Colors and tints in flowers are always more rather than less subtle than you think them. If you have a doubt, make it more delicate—give delicacy the benefit of the doubt. Still, flowers are never weak in color. Subtle as they are, it is the very subtlety of strength. Black will be the most useless color of your palette. Make your grays by mixing your richer colors. A gray in a flower is shadow on rich color, and it must not be painted by negation of color, but by refinement of color.
Sketches.—Make sketches of flowers constantly. Try to carry the painting of a single flower or of a group as far as you can in an hour. Practise getting as much of the effect of detail as possible with as little actual painting of it, and then apply this to your picture.
Get to know your work in studies and sketches, and you will work better in more difficult combinations.
When you have, as you generally will have, still-life accessories to your flowers, rub in quickly the color and values of the vase or what not first, but leave the painting of it till the flowers are done. It will be a more patient sitter than they.
Apply the ways of painting spoken of with reference to still life to the sketching of flowers. Either rub in quickly a frottée and then paint solidly into that, or work frankly and solidly but deliberately to render the characteristic qualities. When you sketch flowers don't take too many at a time; calculate to work not more than an hour and a half or two hours, and have no more flowers in your sketch than you can complete in that time.
When you sketch, quite as much as when you work at more ambitious canvases, get the mass first, especially if the group is large. Then put in the accents which do most to give the character or type of the flower. Make studies of single flowers and sketches of groups. In the study search detail and modelling; in the sketch search relations and relief, effect and large accent.