Try this as an empathy exercise...
...Imagine looking at a web page and hearing it via your ears as a mass of sounds and noises; imagine trying to read a page when each color has a particular sound and tactile sensation, so that you look at a particular shade of orange and feel a literal pressure in your upper back; each picture can be either a little symphony and soothing massage, or a cacophony of raucous sounds and unpleasant pain; imagine trying to pay attention to what the page says while being constantly distracted by the loud pop and crackling-cellophane sound that pops into your mind and whacks you on the back of the neck or pokes you in the stomach every time you glance at the accompanying picture.
Trying to imagine any of this might seem strange, but for a person with synesthesia this type of strange can be routine. In moving towards understanding individual sensory experiences, it helps to remember that each brain is a little different, and each of us sees things a little differently, and sometimes a lot differently.
If you have developed synesthesia yourself you'll have extra insights about aesthetics. The sensory coupling that occurs in synesthesia makes some things apparent that never were before, and design, from interior/exterior decoration to website layout, rarely bears this in mind (so you must be prepared for a few raucous surprises).
If for example you have color-sound coupling, every picture makes a noise, largely due to its color content. Although a webpage like this one is fairly serene -on the whole it has combinations of color that make pleasant ambient sounds; by contrast many social sites are 'raucous', 'loud' and 'crashing', with klaxons going off as things flash at you and a cacophony of different colors that produce a mixture of yelling, banging, honking, crackling and groaning sounds while slapping you round the back of the head in an all-out sensory assault.
I say 'slapping you round the back of the head' because if you also have color- or sound-tactile coupling, these noises can cause feelings of pressure, discomfort or pain in various parts of your body; you may therefore have a highly unpleasant experience and one that almost nobody would consider possible when designing their website. For me, bright yellow sitting right beside pink causes discomfort around the back of the neck, klaxon alarm noises, and a vague feeling of nausea; adding a lime green brings discomfort to the stomach, adding orange brings a loud clatter and hum like a broken fan and discomfort to the shoulders and upper arms. Puce pokes you in the stomach and makes a sound like a cat throwing up under a sofa, so maybe it is intuitively named?
As you can imagine, even looking at some websites (not to mention TV) becomes disorienting and some color (noise) combinations can be truly distressing. You start avoiding places with 'loud' décor. You may avoid a place just because the sound of its name makes you nauseous. You start using all sorts of little apps to block flashy things & pop-ups. At the same time you start surrounding yourself with pictures that make nice noises, and you design your own site carefully so it won't deafen or alarm those with synesthesia.
There is a useful 'clue' about good input to be found here for NH students. You will find most cultural websites (even wikipedia) are designed in aesthetically pleasing ways, even to synesthetes. Whether this is by intuitive or conscious awareness I have no idea, but by contrast, most 'Toilet Empire' sites (for example, sales sites), are a real synesthetic mess with all the loud, uncoordinated racket I mention above. Immediately and without having to read anything, therefore, you can sum up a site from its color content -'loud, shallow & crass', in-your-face, harmonious, or appropriate-to-subject ambience.
Of course, there is a fitting context for 'loud, shallow & crass', for the yellow & green spotty trousers and the purple/orange shirt, with all the attendant klaxons, shouting, one-man-bands, neck-slapping and whoopie-cushion noises. -Clowns for example can use these for slapstick comedy very effectively in the circus ring.
From a synesthetic pov it would be best if they stayed there. One might wonder do the owners of sales sites (and shops) even know they put off customers who are synesthetes due to the 'aesthetic racket', or do they just assume anyone who is that sensitive wouldn't be buying their crap anyway? This much remains unknown. Many of us are blind to what many others perceive.
Can you turn it off? Well yes, you can, with practice; but firstly you're then losing data about a situation and secondly it's too late when it's already taken you by surprise and triggered alarm : )
...I wonder if everyone is now wondering what their avatar sounds & feels like? Every one is different, so you'll have to decipher that for yourselves! Mine makes a faint sine-wave synthesizer noise with a few blue metallic tinkly bits and a very slight crunching, such as the sound of someone quietly munching cookies LOL : )
Did any of you choose your avatars with synesthesia in mind? If not, would you change anything if you did so now? Look around the room you're in -what would the colors sound/feel like with synesthesia?