It's not a linear scale, as the numbers get higher there is less of a difference, hence 4000 looks closer to 3500 than 3000 does, even though they are both 500 apart.
The number Kelvin is CCT (Correlated Color Temperature) which is the color light an object that temperature (in Kelvin*) will emit, so something that has a CCT of 3000K emits light similar to something that is 3000 "degrees" Kelvin. (it is not really degrees because Kelvin is an absolute scale...)
*Kelvin is a scale similar to Celsius but instead of 0 being the temperature water freezes at 0 is the coldest something can get.