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The [[passband]]s most optical [[astronomer]]s use are the [[UBVRI]] filters, where the U, B, and V filters are as mentioned above, the R filter passes red light, and the I filter passes [[infrared]] light. This [[photometric system|system of filters]] is sometimes called
the [[Johnson–Cousins filter system]], named after the originators of the system (see references). These filters were specified as particular combinations of glass filters and [[photomultiplier|photomultiplier tubes]]. [[Michael S. Bessell|M. S. Bessell]] specified a set of filter transmissions for a flat response detector, thus quantifying the calculation of the color indices.<ref name=filters/> For precision, appropriate pairs of filters are chosen depending on the object's color temperature: B−V are for mid-range objects, U−V for hotter objects, and R−I for cool ones.
Color indices can also be determined for other celestial bodies, such as planets and moons:
{| class="wikitable"
|+Color indices of Solar System bodies<ref>https://ntrs.nasa.gov/api/citations/19710009758/downloads/19710009758.pdf</ref><ref name=":0" />
!Celestial body
!B-V color index
!U-B color index
|-
|Mercury
|0.97
|0.40
|-
|Venus
|0.81
|0.50
|-
|Earth
|0.20
|0.0
|-
|Moon
|0.92
|0.46
|-
|Mars
|1.43
|0.63
|-
|Jupiter
|0.87
|0.48
|-
|Saturn
|1.09
|0.58
|-
|Uranus
|0.56
|0.28
|-
|Neptune
|0.41
|0.21
|}
== Quantitative color index terms ==
{| class="wikitable"
|+Quantitative color index terms<ref name=":0">{{Cite journal |last=Neuhäuser |first=R |last2=Torres |first2=G |last3=Mugrauer |first3=M |last4=Neuhäuser |first4=D L |last5=Chapman |first5=J |last6=Luge |first6=D |last7=Cosci |first7=M |date=2022-07-29 |title=Colour evolution of Betelgeuse and Antares over two millennia, derived from historical records, as a new constraint on mass and age |url=https://doi.org/10.1093/mnras/stac1969 |journal=Monthly Notices of the Royal Astronomical Society |volume=516 |issue=1 |pages=693–719 |doi=10.1093/mnras/stac1969 |issn=0035-8711}}</ref>
!Color
!Color index (B-V)
| |||