I didn't find any evidence about native blood.
1900 Mulhall, Logan, OK - all listed as white
John J. Tracey, b. NY April 1864, marr 14 yrs, boiler maker
Sarah N. Gracey, wife, b. MO April 1868, had given birth to six children but only four alive in 1900
Stella, b. KS, Jan 1887
Daniel, b. KS Nov 1888
William A., b. OK Jan 1894
Baby Daughter, b. OK, May 1900, 0/12th
I looked up Sarah Harman and found the following.
1880 Atchinson, Nodaway, Missouri - all listed as white
William harman, b. VA, 52, farmer
Susan A., wife, b. NC, 48
James?, b. MO, 29
William R., b. MO, 17
Elizabeth, b. MO, 14
Sarah N., b. MO, 12
Joshua, b. MO, 9
Thomas K., b. MO, 6
Do you have a copy of Sarah's obituary? If she was a member of a tribe, it might be mentioned there.
More info about her parents.
1900 Rose Hill, Logan, OK - all listed as white
William harman, b. VA Aug 1826, marr 46 yrs, farmer
Susan, wife, b. NC Dec 1830, had given birth to ten children but onlye nine alive in 1900
Eddie Gracy, grandson, b. OK Aug 1896
John L. Gracy, son [but surname could be Harman], b. MO, Aug 1857, widower
1890 Township 18, Logan, OK - all listed as white
William A. harman, b. VA, abt. 1826
Susan A., wife, b. NC, 61
Thomas K., b. MO, 17
Joshua, b. MO, 19
William Addison harman
Born: 2 Aug 1826, VA
Died: 17 March 1916, Oklahoma
Wife: Susan A. Fuller
Source: Porter Family Tree, ancestry.com.
This is a very complete family tree with sources. Most larger public libraries provide free access to Ancestry.com.
I'd look for copies of their obituaries too.
One of their ancestors might have native blood. Successful Searching!