When asked to differentiate traffic signal green, red, and amber using colored cards. The driver can differentiate which color is which, but reports that the red card actually appears "greenish grey" and green card appears "gray-ish". What is the next step?
a) Disqualify the driver
b) Certify the driver for 2 years
c) Refer the driver to a vision specialist for color deficiency evaluation
d) Take the driver to a traffic signal to verify passage of the vision standard