Let’s tackle this puzzle in reverse. HuffYUV and FFV1 are both lossless formats. Neither of them produce any effects on the colors because these formats have zero loss of any color information by definition.
When @chris319 talks about white noise, he is referring to encoder efficiency. As in, when playing back white noise encoded with FFV1, it is very computationally expensive (inefficient) to decode it due to its random nature (no repeating patterns to compress), therefore the file size will be larger, and the playback speed may even slow down if the CPU can’t decode fast enough. Meanwhile, HuffYUV retains fast playback regardless of the video content because its compression method is less aggressive.
Now that we know the characteristics of the two formats, let’s see how they perform in an editing workflow.
FFV1 is a smaller file, but it got that way by burning lots of CPU to achieve higher compression. That means it takes a ton of CPU to decompress it too, and its playback speed will be unacceptably slow for playback and editing on the Shotcut timeline.
HuffYUV is a larger file, but it plays back fast and can be smoothly edited on the timeline.
There are two goals for intermediate files:
- Be as true to the original as possible.
- Make editing faster than the original.
If you’re trying to achieve both goals with a single intermediate file and format, then HuffYUV is your choice (so far) because it is both true and fast. FFV1 is true, but not fast.
The proxy workflow allows you to split these goals up. The intermediate file does not have to be fast because it isn’t used for editing. So using small-but-slow FFV1 is fine. Only your proxy has to be fast, and it can use HuffYUV.
But these are not the only options, hence the context to my statement about the Smithsonian.
My point was that creating lossless intermediates for anything other than Smithsonian artifacts would be overkill. You won’t be able to see the difference, so why burn the disk? This is why ProRes is popular in studios, because it makes smaller files with visually lossless results and faster edits. So my quote is in the context of creating intermediate files directly from the Shotcut interface (and no proxy workflow), where one must choose between ProRes and FFV1. Given those options, I would go ProRes. There are disk savings to be found in humbly admitting that most of our work produced on consumer hardware will not be archived by the Smithsonian for generations to study after us. Perfection is an expensive vanity that 99.9% of our audiences will never notice. 
If you’re more adventurous and do your own transcodes from the ffmpeg command line, then you have yet another option called Ut Video Median which gets you 30% space savings over HuffYUV while retaining the same playback speed. And it’s lossless like FFV1. This is my format of choice for fast intermediates (as opposed to slow intermediates combined with a fast proxy).
To answer your question about suitability based on length of the clip, ideally that should not be a consideration. These formats are chosen because of color requirements, not because of disk space availability. If you have requirements for absolute 100% color fidelity even into the parts of the spectrum that human eyes cannot perceive, then a lossless format is your only option and you give it whatever disk space it demands. If that’s too high a price to pay, then ProRes was invented for a reason and it will serve you well.
FFV1, as stated above, was designed for mastering and archiving at the end of the workflow, not for real-time playback during editing. If your computer can play it back real-time, then more power to you. The compromises described above do not apply to you. For most people, they can’t achieve real-time editing on FFV1 and have to use another format like ProRes, HuffYUV, or Ut Video.
Short version: FFV1 and HuffYUV and Ut Video are all lossless formats. If you’re using proxies, you choose the format that has the highest compression to save disk (FFV1). If you’re not using proxies, you choose one based on fast playback for smooth editing (HuffYUV or Ut Video). If you’re doing everything from the Shotcut interface, HuffYUV is easier to export to. If you’re doing command-line ffmpeg, Ut Video will get you some space savings. But, if you are content with a visually lossless codec (which is good enough for 99.999% of the material out there), then ProRes gets you both disk space savings and decent editing speed.
Everything is a compromise (especially time in production) because humans are only impressed by things that are difficult to achieve. So your challenge is figuring out where you are willing to make those compromises, and you have options for every stage of the workflow. It makes things confusing, but also powerful once understood.