welcome to hcm
thanks for the query
viral infection can change the stool color to dark green color. so it may be gi infection.
if you take food rich in green leafy vegetables like spinach it can also cause green stool
if you are taking iron tabs it can also cause green stool. other cause like malabsorption
,sugar diet also cause it
so wait for 2 to 3 days if it still persists you can consult the physician