Lavender is the most requested soft colour after pink and the one most likely to disappoint on a phone. It photographs beautifully, it looks right in a gallery, and it turns grey the moment it reaches your lock screen. That is not the file's fault, and it is fixable once you know what is happening.
Why purple is the hardest colour on a screen
Two things work against it.
Purple sits at the edge of what a display renders well. It is made from red and blue with almost no green, and small shifts in either move it a long way — towards pink on one side, towards blue on the other. A colour with that little margin is easy to knock off.
And your phone is knocking it off constantly. True Tone adjusts the display's white balance to the room, and Night Shift warms it further on a schedule. Both add warmth, and warmth pushes lavender towards grey-pink or drains it entirely. The wallpaper you chose is not the wallpaper you are looking at in the evening.
Look at any purple image once with both switched off, in neutral light, so you know what the file actually contains before you decide it is wrong.
The shades that survive
Deep violet and plum. The reliable end. Dark enough for a white clock, saturated enough to hold their identity when the display warms.
Dusty lavender. The classic soft version and it works when it leans grey rather than pink. This is the one to look for.
Pale lilac. The difficult one. Light and low-saturation at the same time, which is the combination that disappears. Usable with a dark clock and not otherwise.
Bright or neon purple. Striking and demanding. It holds its colour better than the pale shades and it is the version people replace fastest, because a saturated glow is tiring to look at repeatedly.
The banding problem is worse here
Purple gradients band more visibly than any other colour, for the same reason they shift: there is very little green in them, so the transitions are carried by fewer distinct steps.
A large smooth fade from violet to black is where a compressed file falls apart, and it shows at low brightness in a dark room rather than in the gallery where you chose it.
Prefer images with structure: fabric, sky with cloud, blurred lights, painted texture. Anything that gives the eye detail instead of a pure gradient.
Change the clock, then decide
Tap the time in the wallpaper editor and pick a colour. On a mid or pale lavender, a deep plum or near-black clock is legible where white is not, and the image goes from unusable to good in one step. This is worth doing before you reject any soft wallpaper, because most of the ones people give up on were fine and were being judged with the default white clock sitting on top of them. It takes about five seconds and it changes which half of the category is available to you.
Where it works best
Lavender is a lock screen colour more than a home screen colour, and it is worth knowing why.
App icons contain a great deal of blue and purple already. A purple home screen reduces the contrast that lets you find an app without reading its label, which is the one job a home screen background has.
So the arrangement that works is a lavender lock screen and a considerably darker home screen from the same palette. Blur usually gets you there; if it does not, a deep plum image behind the icons keeps the scheme and restores the contrast.
The night-sky exception
One category of purple image behaves differently from everything above, and it is worth knowing about because it solves most of the problems at once.
Dusk and night-sky photographs — the band of violet between sunset and dark, or a purple-tinted night — are dark rather than pale, structured rather than flat, and they hold their colour when the display warms because the saturation is carried in a small part of the frame rather than across all of it.
They also solve the clock question by accident. The sky is darkest at the top of the frame and lightest near the horizon, so the time sits on the deepest part of the image with no adjustment needed.
And on an OLED screen they are among the cheapest wallpapers you can have, since most of the frame is close to unlit.
If you have tried three lavender wallpapers and none of them survived a week, this is the direction to try next. It is the same colour family doing a completely different job.
Pairing it
Two colours and a neutral, as always.
Cream or warm white as the neutral, which keeps lavender from reading as cold and clinical. Grey as the neutral does the opposite and is the most common way this palette goes wrong.
One accent: sage, dusty rose or a soft gold. Sage in particular is the pairing that reads as designed rather than default.
Avoid pairing lavender with bright pink. They occupy nearby ground and the eye reads two close colours as an accident rather than a choice.
Quick answers
Why does my lavender wallpaper look grey?
Almost always Night Shift or True Tone warming the display. Check both in Settings, Display and Brightness.
Does purple cost more battery than blue?
On an OLED iPhone, marginally, since it lights both red and blue subpixels. The difference is small next to how bright the image is overall.
Can I match the clock to the wallpaper?
Yes, and it works well here because the palette is single-hued. Pick a deeper version of the wallpaper's own colour rather than a contrasting one.
Why does it look better on my friend's phone?
Different display settings, most likely, and different ambient light. True Tone means the same wallpaper genuinely looks different in two rooms.
Where to get it
Preppy Wallpaper: Pink Cute includes the lavender and plum range alongside the pinks, previewed at full size in a phone-shaped frame so you can judge the depth of colour before saving.
Judge it once with Night Shift off. A good share of the complaints about purple wallpapers are complaints about Night Shift.