Vector Blend Modes?

[samplecartography]

I am well aware of the blend mode features when combining a raster layer in mapnik and thanks so much for developing this. I now, however, would like same functionality between two vector layers; largely I am trying to increase the contrast when two low-contrastive features cross. For Example: a park polygon in green is crossed by a very thin stream layer. The stream layer looks great in contrast with the whiter non-park areas [1], however, when the light blue streams cross the darker green polygon of the parks they disappear [2]. I want to be able to set a multiply mode, so vectors can will change color in response to what they are on top of [3,4].

My wish list is long and complicated, but I am glad to have a voice here.

Thanks so much.

[springmeyer]

this has been implemented and is now live in the upcoming TileMill release: 0.10.0. You can test by downloading the TileMill development builds from: https://github.com/mapbox/tilemill/downloads