I have a dataframe, df:

```
 df
     ID  group colour
ID1 ID1 Group1   blue
ID2 ID2 Group1   blue
ID3 ID3 Group2  green
ID4 ID4 Group3  green
ID5 ID5 Group3   blue
ID6 ID6 Group3   blue

df <- structure(list(ID = c("ID1", "ID2", 
"ID3", "ID4", "ID5", "ID6"), group = c("Group1", 
"Group1", "Group2", "Group3", "Group3", "Group3"), colour = c("blue", 
"blue", "green", "green", "blue", "blue")), class = "data.frame", row.names = c("ID1", "ID2", 
"ID3", "ID4", "ID5", "ID6"))

```

I want to split `df` by `group`, and if all the `colour` entries for that group
are `blue`, I want to remove the group.

So in this example, the resulting dataframe would look like:

```
df
     ID  group colour
ID3 ID3 Group2  green
ID4 ID4 Group3  green
ID5 ID5 Group3   blue
ID6 ID6 Group3   blue

```

Group1 would be removed because all the colours listed under Group1 are blue. Group2 is kept because all the colours listed under Group2 are green. Group3 is kept because it has a mixture of blue and green.

I understand that I probably want to do something like:

```
df <- df %>% group_by(group) 

```

But then after that I'm not sure where to go. Can someone please help me on this?