Take average values only across duplicated rows?

I have a data frame with some rows duplicated by a certain column. I want to take the average in those cases, leaving a data frame with only unique values by that column.

mydf <- data.frame("color"=c("blue", "blue", "red", "orange", "green"), 

This is just a minimal reprex - but my 'real' data is much bigger and more complex. How can I make a new data frame that only lists "blue" once, with a value of 20 (since it's the average) - and leaves everything else untouched?

This is a typical example of grouping a data frame by one (or more) columns and summarizing the data in another column.

#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#>     filter, lag
#> The following objects are masked from 'package:base':
#>     intersect, setdiff, setequal, union
mydf <- data.frame("color"=c("blue", "blue", "red", "orange", "green"), 
mydf_2 <- mydf %>% group_by(color) %>% summarize(value=mean(value))
#> `summarise()` ungrouping output (override with `.groups` argument)
#> # A tibble: 4 x 2
#>   color  value
#>   <chr>  <dbl>
#> 1 blue      20
#> 2 green      3
#> 3 orange     2
#> 4 red        1

Created on 2021-07-30 by the reprex package (v0.3.0)

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