For the 'Finds per found date' grid, the colours change at 11 finds, 26 finds, 101 finds and 251 finds....
The 'finds per hidden month' is clearly different, it seems to change the shade every 10 finds...
Hmmm, this seems wrong....we have a challenge here about "3 shades of green", and these are the numbers it states, but looking closer I am not so sure
edit: indeed, the colour changes every extra find. Here is the HTML source of my September finds:
Colour is in ORANGE, Finds in YELLOW. Increasing a find count changes the RGB (red, green, blue) values.... red increased by 2 each time. (first 2 digits), at 'some' point it will be other colours that start changing, I have a single day with 511 finds and it is bright red.
<td class="align-center" style="color: #FFFFFF; background-color: #42c800;">5</td>
<td class="align-center" style="color: #FFFFFF; background-color: #62c800;">15</td>
<td class="align-center" style="color: #FFFFFF; background-color: #66c800;">17</td>
<td class="align-center" style="color: #FFFFFF; background-color: #68c800;">18</td>
<td class="align-center" style="color: #FFFFFF; background-color: #83c800;">39</td>
<td class="align-center" style="color: #FFFFFF; background-color: #56c800;">10</td>
<td class="align-center" style="color: #FFFFFF; background-color: #59c800;">11</td>
<td class="align-center" style="color: #FFFFFF; background-color: #60c800;">14</td>
<td class="align-center" style="color: #FFFFFF; background-color: #56c800;">10</td>
<td class="align-center" style="color: #FFFFFF; background-color: #42c800;">5</td>
<td class="align-center" style="color: #FFFFFF; background-color: #64c800;">16</td>