I could yellow you could yellow he could yellow we could yellow you could yellow they could yellow
V-ing form
I could be yellowing you could be yellowing he could be yellowing we could be yellowing you could be yellowing they could be yellowing
Perfect
I could have yellowed you could have yellowed he could have yellowed we could have yellowed you could have yellowed they could have yellowed
V-ing perfect
I could have been yellowing you could have been yellowing he could have been yellowing we could have been yellowing you could have been yellowing they could have been yellowing
Negation
Simple form
I couldn't yellow you couldn't yellow he couldn't yellow we couldn't yellow you couldn't yellow they couldn't yellow
V-ing form
I couldn't be yellowing you couldn't be yellowing he couldn't be yellowing we couldn't be yellowing you couldn't be yellowing they couldn't be yellowing
Perfect
I couldn't have yellowed you couldn't have yellowed he couldn't have yellowed we couldn't have yellowed you couldn't have yellowed they couldn't have yellowed
V-ing perfect
I couldn't have been yellowing you couldn't have been yellowing he couldn't have been yellowing we couldn't have been yellowing you couldn't have been yellowing they couldn't have been yellowing
Interrogative form
Simple form
could I yellow? could you yellow? could he yellow? could we yellow? could you yellow? could they yellow?
V-ing form
could I be yellowing? could you be yellowing? could he be yellowing? could we be yellowing? could you be yellowing? could they be yellowing?
Perfect
could I have yellowed? could you have yellowed? could he have yellowed? could we have yellowed? could you have yellowed? could they have yellowed?
V-ing perfect
could I have been yellowing? could you have been yellowing? could he have been yellowing? could we have been yellowing? could you have been yellowing? could they have been yellowing?
Interro-negative form
Simple form
couldn't I yellow? couldn't you yellow? couldn't he yellow? couldn't we yellow? couldn't you yellow? couldn't they yellow?
V-ing form
couldn't I be yellowing? couldn't you be yellowing? couldn't he be yellowing? couldn't we be yellowing? couldn't you be yellowing? couldn't they be yellowing?
Perfect
couldn't I have yellowed? couldn't you have yellowed? couldn't he have yellowed? couldn't we have yellowed? couldn't you have yellowed? couldn't they have yellowed?
V-ing perfect
couldn't I have been yellowing? couldn't you have been yellowing? couldn't he have been yellowing? couldn't we have been yellowing? couldn't you have been yellowing? couldn't they have been yellowing?