base colour over hair with tone?

[hairdresser18]

hi, I was wondering if a client has a tone in there hair already say a 10.01, could i just put a 10 over it as it is a base colour cause i have been told that base colours (natural colours) dont have strong warm or cool pigments in the hair as it is neautral, or say a client that has a warm tone in the hair and put a base shade of brown in it. do you know what i mean? thanks