diff --git a/pkg/bot/slack/context.go b/pkg/bot/slack/context.go
index f21f76c..58205f8 100644
--- a/pkg/bot/slack/context.go
+++ b/pkg/bot/slack/context.go
@@ -43,8 +43,7 @@ func (ctx *slackContext) L() *zap.Logger {
 }
 
 func (ctx *slackContext) MessageLimit() int {
-	// https://stackoverflow.com/questions/60344831/slack-api-invalid-block
-	return 2500
+	return 2000
 }
 
 func (ctx *slackContext) StampNames() *domain.StampNames {
@@ -57,21 +56,26 @@ func (ctx *slackContext) StampNames() *domain.StampNames {
 	}
 }
 
-func (ctx *slackContext) sendSlackMessage(channelID string, text string) error {
+func (ctx *slackContext) sendSlackMessage(channelID string, lines []string, color string) error {
 	api := ctx.api
 	return utils.WithRetry(ctx, 10, func(ctx context.Context) error {
-		_, _, err := api.PostMessage(channelID, slack.MsgOptionBlocks(
-			slack.NewSectionBlock(
-				slack.NewTextBlockObject(
-					slack.MarkdownType,
-					text,
-					false,
-					false,
-				),
-				nil,
-				nil,
-			),
-		))
+		var options []slack.MsgOption
+		options = append(options, slack.MsgOptionText(lines[0], false))
+		if len(lines) >= 2 {
+			options = append(options, slack.MsgOptionAttachments(
+				slack.Attachment{
+					Color: color,
+					Fields: []slack.AttachmentField{
+						{
+							Title: "",
+							Value: strings.Join(lines[1:], "\n"),
+							Short: false,
+						},
+					},
+				},
+			))
+		}
+		_, _, err := api.PostMessage(channelID, options...)
 		return err
 	})
 }
@@ -83,17 +87,17 @@ func (ctx *slackContext) pushSlackReaction(message slack.ItemRef, stampID string
 	})
 }
 
-func (ctx *slackContext) reply(message ...string) error {
-	return ctx.sendSlackMessage(ctx.message.Channel, strings.Join(message, "\n"))
+func (ctx *slackContext) reply(color string, message ...string) error {
+	return ctx.sendSlackMessage(ctx.message.Channel, message, color)
 }
 
-func (ctx *slackContext) replyWithStamp(stamp string, message ...string) error {
+func (ctx *slackContext) replyWithStamp(stamp string, color string, message ...string) error {
 	err := ctx.pushSlackReaction(ctx.message, stamp)
 	if err != nil {
 		return err
 	}
 	if len(message) > 0 {
-		err = ctx.reply(message...)
+		err = ctx.reply(color, message...)
 		if err != nil {
 			return err
 		}
@@ -102,21 +106,21 @@ func (ctx *slackContext) replyWithStamp(stamp string, message ...string) error {
 }
 
 func (ctx *slackContext) ReplyBad(message ...string) error {
-	return ctx.replyWithStamp(config.C.Stamps.BadCommand, message...)
+	return ctx.replyWithStamp(config.C.Stamps.BadCommand, config.C.Slack.Colors.BadCommand, message...)
 }
 
 func (ctx *slackContext) ReplyForbid(message ...string) error {
-	return ctx.replyWithStamp(config.C.Stamps.Forbid, message...)
+	return ctx.replyWithStamp(config.C.Stamps.Forbid, config.C.Slack.Colors.Forbid, message...)
 }
 
 func (ctx *slackContext) ReplySuccess(message ...string) error {
-	return ctx.replyWithStamp(config.C.Stamps.Success, message...)
+	return ctx.replyWithStamp(config.C.Stamps.Success, config.C.Slack.Colors.Success, message...)
 }
 
 func (ctx *slackContext) ReplyFailure(message ...string) error {
-	return ctx.replyWithStamp(config.C.Stamps.Failure, message...)
+	return ctx.replyWithStamp(config.C.Stamps.Failure, config.C.Slack.Colors.Failure, message...)
 }
 
 func (ctx *slackContext) ReplyRunning(message ...string) error {
-	return ctx.replyWithStamp(config.C.Stamps.Running, message...)
+	return ctx.replyWithStamp(config.C.Stamps.Running, config.C.Slack.Colors.Running, message...)
 }
diff --git a/pkg/config/config.go b/pkg/config/config.go
index 33d29ac..48c4a69 100644
--- a/pkg/config/config.go
+++ b/pkg/config/config.go
@@ -52,6 +52,8 @@ type SlackConfig struct {
 	//
 	// Trusted workflows are allowed to impersonate the execution user via adding user mention at the start of message.
 	TrustedWorkflows []string `mapstructure:"trustedWorkflows" yaml:"trustedWorkflows"`
+	// Colors sets colors used for reply blocks.
+	Colors Stamps `mapstructure:"colors" yaml:"colors"`
 }
 
 type Stamps struct {
@@ -123,6 +125,12 @@ func init() {
 	viper.SetDefault("slack.channelID", "")
 	viper.SetDefault("slack.trustedWorkflows", nil)
 
+	viper.SetDefault("slack.colors.badCommand", "#dd0204")
+	viper.SetDefault("slack.colors.forbid", "#dd0204")
+	viper.SetDefault("slack.colors.success", "#56c59c")
+	viper.SetDefault("slack.colors.failure", "#dd0204")
+	viper.SetDefault("slack.colors.running", "#e3e4e6")
+
 	viper.SetDefault("prefix", "/")
 
 	viper.SetDefault("stamps.badCommand", "")