Learn English – Need a word to represent the opposite of busy

Will unpretentious work?

Not attempting to impress others with an appearance of greater importance, talent, or culture than is actually possessed: a friendly and unpretentious hotel

in spite of his fame he was thoroughly unpretentious

1.1(Of a place) pleasantly simple and functional; modest.

(Oxford Dictionaries Online)

The coloured edge-pages are called, unsurprisingly, edge painting or fore-edge painting: that's actually already come up on a Stack Exchange site: Why do some books have colors on the edges of the pages?

Print Ninja corroborate that, and even call the speckled effect you see on some books fore-edge splatter. There are even people who do remarkably detailed work.

An edge mark which defines a particular section is called an edge index. This is produced slightly differently (by printing on the face of the page, at the edge, rather than on the closed edge) but has a similar effect.