Following a little sunshine... :

 

 

White peak hold line could be any colour, incl the gradient applied to the spectral display, same with the labels.

Martin,

 

I downloaded Marat's recent work and had a look re your request. It turns out he's changed things quite a lot since I originally implemented the spectrum display, so although I still think you should have a go I also took pity on you ;) 

 

Per the images below I've implemented a 'peak hold' line as well as reintroducing the spectral colour that I used to have in my version. The latter is simply personal preference, or vanity if you prefer, as it happens I quite like Marat's single colour display but while I was messing around with things I thought why not?

 

Did additionally consider adding the relative dbFS lines I had but was running out of [solar] battery and had spent quite enough time trying to find a working SDR unit and set up a machine etc etc (sadly my Mirics-based device appears to have died, so had to find an old 'TV' RTL device instead) therefore this is what you've got.

 

For the present the peak hold line will remain until the spectrum display is toggled off, at which point it's cleared. It could also be easily set to decay over a long period if that was preferable. If it's of interest I can tell you what to alter/add in the requisite file, or maybe just email said file to you....

 

Frequencies removed from images to protect the innocent: