flowers grow longest? what kinds of flowers can grow longest and colourful?

Do you mean long-lasting flowers or how long the plant lives? It's also hard to answer this question without knowing where you live. If you're looking for flowers that last throughout the growing season, you'd be better off with annuals. Flowers like marigolds, nasturtiums, bachelor buttons and cosmos bloom well throughout the growing season.

Most perennial flowers don't bloom throughout the whole growing season but some do bloom longer than others. Perennial cranesbill, certain varieties of daylillies, and foxglove all bloom well for me throughout the season.

If you're looking for long-lived plants, peonies grow well for decades. Hostas and daylillies are also quite long-lived.

If you have a small garden, you might want to consider plants that have interesting foliage as well as colorful blooms. The foliage lasts longer than the flowers themselves. I'm particular to epididium and perennial cranesbill as the foliage turns a nice shade of red in the fall plus it doesn't get ratty after blooming. Hostas come in different color leaves, some with white edgings. Ferns are lovely also.

You don't state what zone or sunlight you have. But a suggestion might be peonies. These like full sun and will grow forever. Some have been around for 100 years!

You might try plants that are self sowing or that spread such as lilies.

I highly recommend going to a local bookstore or nursery to get a book on gardening.

Good luck!