Use 32 bits per pixel by default, since 24 bpp doesn't seem to be a supported option in the RFB 3.8 spec.

lib/units/device/plugins/vnc/util/connection.js

@@ -25,7 +25,7 @@ function VncConnection(conn, options) {
   this._serverWidth = this.options.width
   this._serverHeight = this.options.height
   this._serverPixelFormat = new PixelFormat({
-    bitsPerPixel: 24
+    bitsPerPixel: 32
   , depth: 24
   , bigEndianFlag: os.endianness() == 'BE' ? 1 : 0
   , trueColorFlag: 1