Embed in to web with transparency - everywhere or nowhere

Good day,

We embedded PowerBI reports using example MVC web application with transparent background using following settings:

            var config = {
                type: 'report',
                tokenType: models.TokenType.Embed,
                accessToken: accessToken,
                embedUrl: embedUrl,
                id: embedReportId,
                permissions: models.Permissions.All,
                settings:
                {
                    background: models.BackgroundType.Transparent,
                    filterPaneEnabled: false,
                    navContentPaneEnabled: true,
                    localeSettings: {
                        language: 'en',
                        formatLocale: 'en'
                    }
                }
            };

However, now all report's background became transparent, despit transparency level set there. Originally, without "background: models.BackgroundType.Transparent" transparency didn't work at all.

How this could be taken under control without setting some picture as a background in all non-transparent reports?

Grateful in advance!