Go to TLP documentation » visual assets » illustrations.
Switch the theme to purple.
Click on the button [Inject TLP classes into an illustration], and paste the following illustration:
<svg xmlns="http://www.w3.org/2000/svg" width="60" height="60">
<rect class="tlp-illustration-primary-box"
fill="#92cee5" stroke="#92cee5"
stroke-width="3"
x="5" y="5"
rx="0.6" ry="0.6"
width="50" height="50"/>
</svg>
The generated illustration should be purple, not a mix of blue and purple.