Unfortunately i would think you'd have to go for an annual/bedding plant if you want those kinds of 'mad' colours because perennials are a bit more refined - colourwise.

I was going to suggest Nemesia (a perennial = dies down in winter and pops back up in spring) for the white ones - they are beautifully scented and low growing but the other colours they come in is usually pinks and lilacs so definately not 'mad' !!!

How about planting Nasturtiums? They're definitely mad, and you can get them in various colours, including red. They do seed themselves, although they're annuals.

By the way, Nemesia is now available in deep pink/red/blue/maroon/purple shades, as well as the paler ones. It's not hardy, though.

Like minds Spritz I thought of Nasturtiums too.
A Phlox subulata such as 'scarlet flame', there is also a white variety, or a Rockery Penstemon rubicola 3" high and crimson flowers both give off a fragrance. Another deep red is Helianthemum Fireball.

Pinks come in red as well as white and the expected pink. They smell nice, but the flowers come up a bit higher than 3 inches.

The ID question yesterday that showed a pic reminded me - there's a creeping Persicaria called "Red Dragon" that has dark red leaves. Not quite as showy as a scarlet busy lizzie, but liable to be there for more of the year.

Hi Beatie Pinks - Dianthus Alpinus grow just above the ground at about 2-4"" I have several one is Dianthus Alpine Myrtinervius.

Snap Drc, I was going to say Dianthus, lovely old fashioned 'pinks', they come in red, white & pink. Sorry Beattie, just read your suggestion. If you go to your GC you will find many plants in flower and you can make your choice. I have just purchased a Potentilla, Fireball its a gorgeous dark red.

The helianthemums are a good idea, Denise, they can be vivid and flower prolifically from spring to autumn nonstop !

Yes they are, I love mine Louise.