Peyton Manning has the highest completion percentage by a Colts quarterback in a game with 20+ passing attempts, at 85.3 percent versus the Jaguars on December 18, 2008.

which qb has the highest comp% in a game colts with a minimum of 20 attempts
Interpreted as:
Which qb has the highest comp% in a regular-season game colts with a minimum of 20 passing attempts?
12/18/2008Manning11/12/1967Unitas12/14/2003Manning9/25/2005Manning11/25/2004Manning10/29/2006Manning10/11/2009Manning10/16/1994Harbaugh12/7/2008Manning11/25/2018Luck12/4/2011Orlovsky9/27/2020Rivers12/18/2006Manning12/23/2007Manning9/28/2003Manning10/22/2000Manning11/16/1997Justin9/21/2014Luck11/18/2018Luck11/8/2004Manning9/23/2001Manning12/5/1999Manning9/11/1994Harbaugh85.385.083.382.682.182.181.881.881.381.181.181.080.680.080.080.080.079.579.379.379.379.379.2
NAMEDATETMOPPPCTATTCMPYDSAVGTDTD%INTINT%SCKSCKYRATE
Peyton ManningPeyton Manning12/18/2008INDIND@JAXJAX85.3342936410.738.800.000140.7
Johnny UnitasJohnny Unitas11/12/1967BALBAL@ATLATL85.0201737018.5420.000.0158.3
Peyton ManningPeyton Manning12/14/2003INDINDvsATLATL83.330252909.7516.700.019146.5
Peyton ManningPeyton Manning9/25/2005INDINDvsCLECLE82.623192289.900.014.30089.9
Peyton ManningPeyton Manning11/25/2004INDIND@DETDET82.128232368.4621.400.000141.4
Peyton ManningPeyton Manning10/29/2006INDIND@DENDEN82.139323458.837.700.000129.2
Peyton ManningPeyton Manning10/11/2009INDIND@TENTEN81.844363097.036.812.300109.2
Jim HarbaughJim Harbaugh10/16/1994INDIND@BUFBUF81.822182069.429.100.000136.0
Peyton ManningPeyton Manning12/7/2008INDINDvsCINCIN81.332262778.739.400.000134.0
Andrew LuckAndrew Luck11/25/2018INDINDvsMIAMIA81.137303439.338.125.4110109.8
Dan OrlovskyDan Orlovsky12/4/2011INDIND@NENE81.137303539.525.412.7215113.2
Philip RiversPhilip Rivers9/27/2020INDINDvsNYJNYJ81.0211721710.314.800.000125.6
Peyton ManningPeyton Manning12/18/2006INDINDvsCINCIN80.636292827.8411.100.010136.3
Peyton ManningPeyton Manning12/23/2007INDINDvsHOUHOU80.035283118.938.600.012132.3
Peyton ManningPeyton Manning9/28/2003INDIND@NONO80.0252031412.6624.000.019158.3
Peyton ManningPeyton Manning10/22/2000INDINDvsNENE80.0201626813.4315.000.000158.3
Paul JustinPaul Justin11/16/1997INDINDvsGBGB80.0302434011.313.300.0220125.0
Andrew LuckAndrew Luck9/21/2014INDIND@JAXJAX79.539313709.5410.300.025140.4
Andrew LuckAndrew Luck11/18/2018INDINDvsTENTEN79.3292329710.2310.300.000143.8
Peyton ManningPeyton Manning11/8/2004INDINDvsMINMIN79.329232689.2413.800.014144.8
Peyton ManningPeyton Manning9/23/2001INDINDvsBUFBUF79.3292342114.5413.826.913129.6
Peyton ManningPeyton Manning12/5/1999INDIND@MIAMIA79.329232609.013.426.921986.8
Jim HarbaughJim Harbaugh9/11/1994INDIND@TBTB79.224192068.600.014.21585.1
Jim HarbaughJim Harbaugh9/7/1997INDINDvsNENE78.938302416.300.000.052793.1
Peyton ManningPeyton Manning12/12/2004INDIND@HOUHOU78.833262989.026.100.0217124.5
Results may be incomplete. StatMuse has complete game-level data for completion percentage and passing attempts going back to the 1950 season.

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