Black Badges did commemorate Jim Clark.

[Sadbrewer]

I don’t know if this adds anything to the discussion, but here’s what Graham Arnold wrote in 1981 in ‘The Lotus Elan and Plus Two Buyers Guide’, published by him as the then owner of the business misleadingly called ‘Club Lotus’:

“BLACK BADGE MODELS. Some time after Jim Clark was killed the company changed over from the traditional Lotus yellow and green bonnet badge to a black and silver design. This followed the similar lead of Rolls Royce who changed their badge from red to black on the death of Rolls.”

My Plus 2 was manufactured in May 1968 and registered on 18 June 1968. It was photographed wearing a black badge in the Summer of that year so presumably it was fitted from new.

Many thanks Lotusian
Effectively that further invalidates GA's later statements of 'cheapness' and 'Black Badge Baloney'.
I had intended to reply soon to some of the comments, particularly as Brian made an interesting and valid comment around the August date of the factory press releases in the newspapers.
Everything I wrote in the original piece was corroborated by other testimony, from the people responsible at the time answering direct questions or by press releases....nothing is speculation.

I will though speculate now...
.Brian's point of 'why August' was a valid question.
John Berry has told us he suggested it to Colin on his return from Vilars and got the go ahead.
Martin Long has confirmed it took two weeks to organise the black badges from Fattorini's....but we don't know when the first ones were actually fitted. I have looked for John Spurgeon ( Production Manager) unfortunately with no luck.
Roger Putnam has confirmed a publicity photo of a July 1968 Europa with a black badge.
I think the badges were probably fitted shortly after being received from Fattorini's, which would be roughly early or mid May 1968.
Lotus will have had a number of cars built ( some at dealerships/ some in kit form) and a number of cars already in transit to overseas markets...June and July was notoriously slow for new (UK) car sales in those days...buyers wanting the new number plate suffix letter.
I think the August press release was made when they were reasonably sure the existing stock had been sold
in the UK or already delivered to the overseas market.