Maintain selected color when adding to palette

[borboss]

Not a major change; just uses the last selected color for the new color when creating a palette.

In most programs (even ms paint), when adding a color to a palette it doesn't reset the color to white. Instead, it keeps the selected color.

See GIF of changes:

.

[borboss]

Here's how it was before. Note the reset to white:

[mbrlabs]

Thanks!