I could discolour you could discolour he could discolour we could discolour you could discolour they could discolour
V-ing form
I could be discolouring you could be discolouring he could be discolouring we could be discolouring you could be discolouring they could be discolouring
Perfect
I could have discoloured you could have discoloured he could have discoloured we could have discoloured you could have discoloured they could have discoloured
V-ing perfect
I could have been discolouring you could have been discolouring he could have been discolouring we could have been discolouring you could have been discolouring they could have been discolouring
Negation
Simple form
I could not discolour you could not discolour he could not discolour we could not discolour you could not discolour they could not discolour
V-ing form
I could not be discolouring you could not be discolouring he could not be discolouring we could not be discolouring you could not be discolouring they could not be discolouring
Perfect
I could not have discoloured you could not have discoloured he could not have discoloured we could not have discoloured you could not have discoloured they could not have discoloured
V-ing perfect
I could not have been discolouring you could not have been discolouring he could not have been discolouring we could not have been discolouring you could not have been discolouring they could not have been discolouring
Interrogative form
Simple form
could I discolour? could you discolour? could he discolour? could we discolour? could you discolour? could they discolour?
V-ing form
could I be discolouring? could you be discolouring? could he be discolouring? could we be discolouring? could you be discolouring? could they be discolouring?
Perfect
could I have discoloured? could you have discoloured? could he have discoloured? could we have discoloured? could you have discoloured? could they have discoloured?
V-ing perfect
could I have been discolouring? could you have been discolouring? could he have been discolouring? could we have been discolouring? could you have been discolouring? could they have been discolouring?
Interro-negative form
Simple form
could I not discolour? could you not discolour? could he not discolour? could we not discolour? could you not discolour? could they not discolour?
V-ing form
could I not be discolouring? could you not be discolouring? could he not be discolouring? could we not be discolouring? could you not be discolouring? could they not be discolouring?
Perfect
could I not have discoloured? could you not have discoloured? could he not have discoloured? could we not have discoloured? could you not have discoloured? could they not have discoloured?
V-ing perfect
could I not have been discolouring? could you not have been discolouring? could he not have been discolouring? could we not have been discolouring? could you not have been discolouring? could they not have been discolouring?