Papers differ in whiteness. Today's press sheets are typically manufactured with Optical Brightening Agents (OBAs). The OBA level will vary among papers. Higher OBA papers will appear brighter white under lighting where UV is present.
L*a*b* measurements under M1 will show higher -b* numbers as OBAs increase.
White Point Targets
GRACoL 2006: M0 ~No OBAs or UV ~ L*95, a*0, b*-2
GRACoL 2013: M1~ OBAs with UV ~ L*95, a* 1, b* -4
Bright White Paper: M1 ~ High OBAs with UV ~ b* -8 minimum