library(tidyverse)
data%>%
  group_by(id)%>%
  filter(1==length(unique(colour)),!duplicated(colour))
# A tibble: 4 x 3
# Groups:   id [4]
  id    colour subgroup 
  <fct> <fct>  <fct>    
1 1     red    lightred 
2 2     blue   lightblue
3 3     red    lightred 
4 5     green  darkgreen

使用基本R:

 subset(data,as.logical(ave(colour,id,FUN=function(x)length(unique(x))==1& !duplicated(x))))
  id colour  subgroup
1  1    red  lightred
2  2   blue lightblue
4  3    red  lightred
8  5  green darkgreen