Of course, icing can be hard to see at night. Especially in a single or twin without ice lights. Shining the torch out the window is the best you can do.
Clear ice can be hard to detect visually.
However, in flight ice builds up on the smaller leading edges before the large ones. Thus ice will form on the tail and propeller leading edges before being detected on the wing leading edges. So if you can see ice building on the wing leading edge, there will often be more on the tail. Something to encourage you to get out of those conditions.
For pilots of the Piper aircraft or similar with the OAT probe extending from the windscreen, the initial indication of ice formation will be seen on the forward side of the probe.
This can also be used to judge when to activate the de-ice boots on aircraft that have them.
Regards,
DFC