There have been changes to the layout of this site. I would start from 'Species' on the selection bar that runs across, near the top of the page, and then choose 'Identification' in the drop-down list that appears.
There are around 2500 moth species as opposed to only 58 regular butterfly species in the UK. Thus, an 'unknown unknown' is far more likely to be a moth than a butterfly!
I usually start by searching in Google Images. When searching, it is important not to be too specific at the first pass. Simple search terms such as "pale moth uk" will probably find something like what you are looking for. If you need to go further, then stick to simple words. "Aqua" can lead to all sorts of false paths, such as water, sea, etc. For colours, just use green blue, etc.
If you don't find what you want at first, then look at the descriptions of what you do find, since they can suggest appropriate terms to take you in the right direction - there are plenty of winged insects, other than moths or butterflies, and it could be one of those.
If it looks as though it's a moth, then
https://ukmoths.org.uk/ has various search boxes, to help you home-in and find more details of your suspect. Don't forget to check aspects such as flight times, to make sure your identification is plausible.
Remember too that 'mimicry' is frequently found in the insect world (and elsewhere). Lots of harmless species 'pretend' to be something less desirable as prey - there are moths that look like hornets for example.
It's not easy, so never be afraid to ask for help in the forums on this site
Mike