Solid line = floor (spellings that unambiguously belong to the group). Shaded band up to the dashed edge = ceiling (the most it could reach if every ambiguous spelling counted here).
Colt has been climbing in recent years. All-time it's been given to 30,954 U.S. babies, the 494th most common name by sound today, peaking at 2,033 in 2019, with 1,317 in 2025.
By sound, Colt also includes the spellings Kolt.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).