There is no connection between the region names and the theme of the names. The names of the regions are actually based off of Japan, except for Unova, which is based from New York City, and Kalos, which is based from France. The theme of Kanto is colors, starting with Palet Town, as a Palette holds colors and the towns that follow are all colors (i.e. pewter, cerulean, vermillion, etc.). Johto has a theme of trees and plants. It starts with New Bark, as in bark from a tree, then the towns follow, (i.e. Cherrygrove, Ecruteak, Mahogany, etc.). Hoenn is just a two words combined that describe the town (i.e. LavaRidge, LittleRoot, LillyCove, MossDeep, Ever Grande, etc.). Sinnoh has no overall theme, but some believe it follows the same formula as hoenn. Unova is based off of clouds or anything related to clouds (i.e. Nimbasa[nimbus cloud], icirrus[cirrus cloud], mistralton[mist], accumula[clouds accumulate], striaton[stratus], driftveil[clouds drift], opelucid[lucidity], etc.). Last but not least, Kalos. On Bulbapedia, they said that these towns were based off of ingredients used in fragrances. I don't know, but I hope I helped.