Unfortunately, there is No SharePoint OOTB way to change the complete background color of list view. But you can change the background color of item rows/tiles using JSON Formatting.
Sample JSON:
{
"$schema": "https://developer.microsoft.com/json-schemas/sp/v2/tile-formatting.schema.json",
"height": 73,
"width": 254,
"hideSelection": false,
"fillHorizontally": true,
"formatter": {
"elmType": "div",
"attributes": {
"class": "sp-card-container"
},
"children": [
{
"elmType": "button",
"attributes": {
"class": "sp-card-defaultClickButton",
"role": "presentation"
},
"customRowAction": {
"action": "defaultClick"
}
},
{
"elmType": "div",
"style": {
"background-color": "lightblue"
},
"attributes": {
"class": "ms-bgColor-white sp-css-borderColor-neutralLight sp-card-borderHighlight sp-card-subContainer"
},
"children": [
{
"elmType": "div",
"attributes": {
"class": "sp-card-lastTextColumnContainer"
},
"children": [
{
"elmType": "p",
"attributes": {
"class": "ms-fontColor-neutralSecondary sp-card-label"
},
"txtContent": "[!Title.DisplayName]"
},
{
"elmType": "p",
"attributes": {
"title": "[$Title]",
"class": "ms-fontColor-neutralPrimary sp-card-content sp-card-highlightedContent",
"role": "heading",
"aria-level": "3"
},
"txtContent": "=if ([$Title] == '', '–', [$Title])"
}
]
}
]
}
]
}
}
In above JSON, I have added below code manually in JSON code provided in Gallery view by default (you can change the color as per your requirements):
"style": {
"background-color": "lightblue"
},
Output: