Index means that you have a set limited amount of colours. Pixelart has an index usually. The general limit is 256 colours, but for most pixelart people use less. A lot less.
This is an Image by a french Demoscener who went by the handle Ra.
This uses 256ish colours, long ramps. And this is what you call indexed painting. You set up your colours beforehand and then you work from there, using tools like tinting, darken/lighten, some blur, and so on. There is still a lot of pixel level control, but not as much as in what we would call pixelart usually.
Yours is not index painting, seeing as it has 7000+ colours. I reckon you did this in Photoshop or some similar paint packaged and ignored the pixel level detail in most cases. Also HD does not mean A LOT OF COLOURS necessarily. It means High Definition, as in High Resolution. These look like they are perhaps 24x24 pixels or so each. That is hardly HD. At a size like this every pixel counts. And things like contrast are very important.
On quite a few of them the red background colour fights with the icon. Most notably with the 2 bottom left saw sword things. Red tends to push itself into the foreground, blue receeds. The red and greys have very close perceptive values, so the eye finds it hard to focus on them.
All of these would benefit from less colours, better colours, and better contrast. Some of them are also quite different styles. Like the ones with the relatively harsh outlines in some places.
