@teofilosalgado can you please share the URL to the mapservice you are using?

@teofilosalgado also what format is being used? Default of esri-leaflet should be 'png24' but the white background makes me wonder if a 'jpg' format is being used.

And a demo to help us debug would speak 1,000 words, too.

(if possible, create a jsbin that demonstrates the problem)

@gavinr Sure! The URL is http://sistemas.gt4w.com.br/arcgis/rest/services/SICARF/Camadas/MapServer/

@jwasilgeo I left format to the default settings, as you said, 'png24'.
The snippet below could reproduce the problem in any enviroment, it's quite simple:

const map = L.map('map', this.config)
const mapServer = esri.dynamicMapLayer({
        f: 'image',
        url: 'http://sistemas.gt4w.com.br/arcgis/rest/services/SICARF/Camadas/MapServer',
        transparent: true,
        maxZoom: 16,
        minZoom: 3,
        layers: [6]
})
mapServer.addTo(map)

I will create an JSBin and reply it's link here ASAP.

@jwasilgeo https://jsbin.com/timusiviqa/1/edit?html,output

@teofilosalgado thank you for the extra info and for the jsbin.

Can you try also this property in your layer options?

format: 'png32'

I think that works better and seems to provide the visual output you want. Must just be png24 vs png32.

@jwasilgeo it worked like a charm! Thank you! Me and my team were stuck with this problem for days!

I'm very happy to hear the good news. Do you happen to have any feedback or suggestions on improvements to the documentation, such as for the format option?

would it help to just default to "png32" 🤷‍♂

I agree with @jgravois, I really thought png24 could handle transparency without any problems. We are used to correlate png (in any flavor of it's specification) with transparent images. Maybe adding a note on png32/png24 in the documentation would be helpful, or even explaining why this happens.

L.esri.dynamicMapLayer now defaults to png32 for the format parameter. Thank you @pmacMaps. See PR #1202.