Romex IS NM - NM means Non Metallic. Used to be NMW and NMD for non metallic wet and non metallic dry..
Current product is NMD90 (90C temperature rated) NMWU is direct burial cable. Loomex (Noramco) is a term replacing Romex (Southwire) in many areas - and there is a red sheithed Loomex called Heatex for use in 240 volt electric heating applications that is NMD90 2 wire with black and red conductors plus bare ground - no neutral. - referred to as Heatex. Commonly the NMD is white, the NMW is black and the Heatex is red. Other companies have different colour coding.
One "standard" is white for 14, yellow for 12, orange for 10, and black for 6 and 8, and gray for NMWU direct burial.
Blue #14 is used in Ontario for Arc-Fault protected circuits. Red 14/2 and 12/2 is used in Canada for heating circuits (used to be Orange back before 2001 when "xtra-colour" Romex hit the market from Southern Cable in Canada
So - DO NOT assume just because a wire is white, or black, or orange, it is a particular guage of wire!!!!