Back in early April “Jiahe” commented on my post “
The Great Blue Challenge” that he had used Pilot Color Eno blue lead and that it had faded rather quickly. I was initially surprised at this, and my surprise turned to embarrassment when it was pointed out that the lead container carries a warning about fading, as shown below.

Jiahe then challenged me to do some fade testing (or light fast testing) on the various blue leads that I had, and I reluctantly accepted.
So, firstly, the blue leads that I have.
In order, left to right:
Pilot Color Eno
Uni ~ish (“Mint Blue” is the colour selected for this test)
Uni Color
Staedtler Mars Micro Color
Faber-Castell TK Color
Pentel (PPB)
Pentel Ain
Maybe someday a pencil company will spell colour correctly? .i.e. my way.

I scribble-coloured a rectangle of about 5cm long and 1cm wide for each lead, and then cut the paper into three long strips so that they could be stored separately but re-assembled back together. The strips were labelled “sun”, “some” and “dark”, and were exposed as below:
“Sun” = taped up in a north facing glass window (remember I’m in the southern hemisphere) to get a good dose of sunlight throughout the day. The window glass is untinted and does not have any anti-UV or other treatments, but it is autumn so some days are nice and sunny, but others overcast or rainy.
“Some” = put on the desk in my office at home. The blinds are mostly closed so there is not a lot of natural light.
“Dark” = kept in a closed cupboard, no exposure to light, but exposed to the air.
The Results (all colour photos below are clickable for high res)
Week 1

Yarrrrr???!!! Where has Pilot Color Eno gone? The “sun” exposure has completely faded and disappeared. At first I did a double take – did I forget to colour in that part? Had I aligned my three test-strips of paper incorrectly? If you look really hard you can see some remnants, but for all intents and purposes Color Eno has completely gone. The “some” exposure has had a little fading, though not much.
There is a hint of fading on “sun” for Uni ~ish, but Uni Color has definitely changed. The “sun” exposure getting lighter and greyer, and “some” getting a little lighter. All the other samples are essentially unchanged.
Week 2
Well the sun has done for Uni Color and it’s a goneburger. The “some” exposures for Pilot Color Eno and Uni Color are clearly starting to fade. Note that unlike Uni Color, Uni ~ish Mint Blue is holding up fairly well although the “sun” exposure is starting to show some fading. All the others are looking good.
Week 3

Basically more of the same. The “some” exposure for Pilot Color Eno appears to be on its last legs.
Week 4 – Final Results

Four of our blue leads showed little to no fading and have completed the lightfastness test with flying colours. Full marks to Staedtler Mars Micro Color, Faber-Castell TK Color, Pentel PPB and Pentel Ain. Fifth out of seven is Uni ~ish Mint Blue which has shown some fading for the ‘sun’ exposure, and a little fading for the ‘some’ exposure. Bringing up the rear, and a long way behind, are Uni Color and Pilot Color Eno. Pilot Color Eno 'sun' disappeared in week 1. Perhaps you artists out there can tell me of some use for special disappearing blue leads. Secret agents?
You will need to read my various blue lead postings to choose a lead for you that has the right combination of hue, lightfastness, strength, erasability, etc, but for me personally there is Pentel and then there is…nothing.
No, NO,
NO! Don’t ask me to repeat all this for red, green or any other blasted colour. It ain't happen'n.