Making patch and background transparent in pcolor plot

Hello,

I am creating maps of data using pcolor and vectors overlaid with Quiver. I need to have the land and the figure background transparent so these can be overlaid over other maps. I've been painting the land black and the using findobj to convert the black patch to transparent, but it ends up being white when I save the figure as a png. Any suggestions?

thanks for any help!

Marina

V=(0:0.05:1);

load('mycmap_oscar','mycmap_oscar')

fig = figure;

m_proj('mercator','longitudes',[-96,-77],'latitud',[1,20]);

hold on

m_pcolor(long,lati,speed); shading interp;

colormap(mycmap_oscar);

fig = m_quiver(long,lati,outstrct.u(idx_lon,idx_lat),outstrct.v(idx_lon,idx_lat),2,'k','LineWidth',0.7);

m_gshhs_h('patch',[0 0 0]); % searches for the GSHHS database in /m_map/private. Sets land to black.

m_grid('box','off', 'LineStyle','none','xticklabels',[],'yticklabels',[],'xtick',[],'ytick',[]);

caxis([0.01 0.7])

set(findobj(gcf,'FaceColor',[0 0 0]),'FaceAlpha',0,'FaceVertexAlphadata',0)